Free WorkKeys Practice Test for 2024

Free WorkKeys Practice Test for 2024

The ACT ® WorkKeys evaluates your work-related “soft” and “hard” skills to predict your learning capabilities and job performance. Scoring high on the WorkKey exam will showcase your potential as an employee.

The test includes 8 sections, each with several difficulty levels that integrate previously assessed abilities. For example, in level 6, you will need the skills from levels 4 and 5.

Our free WorkKeys practice test will guide you through every section, help you locate your weak areas, and provide detailed solutions for all questions.

Why should I practice for the ACT WorkKeys Exam?

David, ACT WorkKeys Expert at JobTestPrep
Have a question? Contact me at:

ask_the_team@jobtestprep.com

WorkKeys Practice Test

We will start the WorkKeys practice exam with the first three sections of the assessment, which make the mandatory requirements for receiving the ACT WorkKeys NCRC (National Career Readiness Certificate):

Applied Mathematics – the ability to apply mathematical reasoning, critical thinking, and problem-solving techniques to work-related problems.

Graphic Literacy – the ability to interpret, apply, or compare information presented graphically (charts, graphs, etc.).

Workplace Documents – the ability to read and use written text such as memos, letters, and instructions.

Earning the NCRC will require passing these sections at a score level of 3 and higher.

Read our WorkKeys Test Scores Guide to better understand the requirements.

Afterwards, we will continue with the additional sections of the test –

As in the real test, each section of the WorkKeys practice exam has various difficulty levels, which are explained below.

The first section we will cover is Applied Mathematics.

How can I improve my performance in the WorkKeys Test?

WorkKeys Practice Exam — Applied Mathematics Sample Questions

The WorkKeys Applied Mathematics section has five difficulty levels, ranging from 3 to 7.

You will have 55 minutes to answer 34 questions.

Just like in the actual test, you are welcome and advised to use a calculator, pencil, and pen while solving the WorkKeys practice exam.

WorkKeys Applied Mathematics Test – Level 3 Question

A college fraternity planned a three-day study marathon. On the first day, they studied 75% of the time, ate for 3 hours, and slept the rest of the time. On the second day, they studied 50% of the time, ate for 4 hours, and slept the rest of the time. On the third day, they slept 1⁄3 of the time. How many hours in total did the fraternity members sleep during the three days?

Note that one day contains 24 hours.

A. 15 hours

B. 19 hours

C. 24 hours

D. 38 hours

Answer : the correct answer is B.

Calculate the number of hours the fraternity slept every day:
Start by converting the percentages into absolute hours.

First day (24 hours):

The students slept for 3 hours on the first day.

Second day (24 hours):

Third day (24 hours):

Total number of hours spent in sleep: 3+8+8 = 19

The correct answer is B

WorkKeys Applied Mathematics Test – Level 4 Question

Dan took a two-hour walk around a round lake. The radius of the lake is 6 feet. What was Dan's average speed?

A. 2π feet\hour

B. 16π feet\hour

C. 12π feet\hour

D. 24π feet\hour

Answer : the correct answer is B.

Any time we need to calculate the speed, we should use the formula time x speed = distance:

The time is given. Now, in order to calculate the speed, first find the distance.

The lake is round with a radius of 6 feet. Accordingly, if Dan took a walk around the lake, the distance he walked is also the perimeter of the lake.

Therefore, use the formula of a circle’s perimeter in order to calculate the perimeter of the lake:

Therefore, Dan's average speed is 6π.

If you chose any other answer, review the solution and your calculations.

The correct answer is B

Since time is short, and the questions increase in difficulty through the test, we recommend you practice the test using different tools and see which ones help you answer faster. Calculators, formulas, and scratch pads are valuable, and it is highly recommended that you put them to use – even the simplest calculations should be quickly performed with a calculator to avoid mistakes and to work as methodically as possible.

WorkKeys Applied Mathematics Test – Level 5 Question

A pencil is sketched using a rectangle and an isosceles triangle. The length of the pencil is 12 inches. The length of the rectangular section is five times longer than its width, and the height of the triangle is 2 inches. What is the perimeter of the pencil?

A.

B.

C.

D. Insufficient information

Answer : the correct answer is B.

The full measurements of the pencil are:

Use the image to see if you understand the correct answer.

In order to solve this problem, calculate the length of all outer sides of both the rectangle and the triangle.

From the given information, it is known that the total length of the pencil is 12 inches, and the height of the triangle is 2 inches; therefore, the length of one side of the rectangle is: 12-2 = 10 inches.

Given that one side of the rectangle is five times longer than the other:

And, since opposite sides of a rectangle have the same length (or “congruent”):

In an isosceles triangle, the height is perpendicular to the base and divides the base into two equal parts, thus the sides of the triangle can be calculated using the Pythagorean Theorem:

The perimeter of the pencil is:

If you chose answer (A), you probably confused the base and the other sides of the triangle. If you chose answer (C), you probably forgot to divide the base by two, and if you chose answer (D), review the solution.

The correct answer is B

WorkKeys Applied Mathematics Test – Level 6 Question

Dan is diving in El-Nido in the Philippines. He starts his dive from a boat five meters above sea level (0 meters), and he is descending two meters each minute.
Which of the following describes Dan’s dive as a function of elevation and time?

A.

B.

C.

D.

Answer: the correct answer is A.

The line equation: y = mx + n;
m = slope,
n = the intersection point between the line and the y-axis.

The graph is the elevation of Dan relative to the ground as a function of time. The x-axis represents time. The y-axis represents elevation; Dan was five meters above when he dove: i.e he had an elevation of 5 meters, at time = 0 minutes. Therefore, the beginning point is (0, 5).

Dan is diving down at a rate of two meters per minute. This means that the slope is: m = -2 meters/minute

Find the linear equation describing Dan’s dive, using the information you found:

Now find another one or two points and find a graph that maintains these points:

The only graph containing these points is A.

If you chose answer (B), note that the graph starts at the origin. If you chose answer (C), note that the graph’s slope is -1. If you chose answer (D), note that the graph’s slope is -1, and it starts at the origin.

The correct answer is A

Whenever possible, try to simplify the question as much as you can. Not all questions require long equations and solving for variables. Many questions can be answered by using the answers to substitute the unknown factors in the answers, thus eliminating distractors. Consider the previous question (level 6) – and see if you can solve it by common logic (where the graph begins, and how steep should the incline be).

Let’s review the final level of Applied Mathematics.

WorkKeys Applied Mathematics Test – Level 7 Question

Nancy is planning a ring-shaped pool for a new hotel in Florida. The outer diameter of the pool is 100 feet. If the pool has an area of square 1600π ft., which of the following is its inner diameter (the diameter of the dry area)?

A. 60 feet

B. 70 feet

C. 80 feet

D. 90 feet

Answer: the correct answer is A. The outer diameter is 100 feet. Therefore, the radius of the entire shape is 50:

The total area of the pool is the area of the whole shape minus the dry area (da):

The length of a radius can be only positive; therefore, r = 30.

The diameter (d) equals two times the radius:

d = 2r = 2x30 = 60.

The inner diameter is 60 ft. If you chose any other answer, review your solution.

The correct answer is A

Why is practice important for the WorkKeys Exam's Applied Math?

Once we have completed the Applied Mathematics section, we will move on to the next section – Graphic Literacy. This section also requires mathematical abilities, but this time mainly concerns graphs and tables, which increase in difficulty with the amount of data and requirements in each question.

WorkKeys Practice Exam — Graphic Literacy Sample Questions

The WorkKeys Graphic Literacy section has five difficulty levels, ranging from 3 to 7.

You will have 55 minutes to answer 38 questions.

WorkKeys Graphic Literacy Test – Level 3 Question

The following chart shows the average temperature, in °F, for Monday (orange), Tuesday (yellow), and Wednesday (blue). What was the approximate temperature on Wednesday?

A. 20°F

B. 80°F

C. 70°F

D. 60°F

E. 50°F

Answer: the correct answer is B.

According to the chart, the temperature on Wednesday (represented by the blue bar) reached approximately 80°F.

The correct answer is B

WorkKeys Graphic Literacy Test – Level 4 Question

The following diagram shows the 800 m men's race results at the 1976 Summer Olympics. What was the running time for the runner from India?

A. 1:43.86

B. 1:44.12

C. 1:54.44

D. 1:45.77

E. 1:48.39

Answer : the correct answer is D.

According to the diagram, Sri Ram Singh was the runner from India. His running time is marked as 1:45.77.

While we are sometimes keen to dive deep into the graph and read the introduction, understanding what is that's in front of us may be time-consuming. A simpler method would be to read the question and go directly to the answers, which will help you look strictly for what you need. In the first question – looking at the answers will quickly guide you to each graph.

This is a very useful method for low and high-level questions and should be incorporated into your practice to decide by how much it increases your score. However, ensure you read any notes or essential pieces of information if presented.

Let’s continue with an increasing level of Graphic Literacy questions!

WorkKeys Graphic Literacy Test - Level 5 Question

Below is a pie chart depicting the viewing habits of different age groups in relation to different genres in a specific movie theatre. Each segment of the pie represents about 4% of all movies viewed in an average year. Each segment represents a genre according to the segments key. Each chart is divided into four parts so that each part describes a different age range. These age ranges are represented by different rectangles at the side of the chart.

For example: 75% of the movies viewed by 4–12 year olds are animated films.

Which age group watches fewer movies than any other?

A. 4-12

B. 13-20

C. 21-45

D. 46-80

E. They all have the same proportional viewership

Answer: the correct answer is A.

Because each segment of the chart represents a certain percentage of the films viewed, and because all segments are equal, the age group with fewer segments watches fewer movies.

Counting the number of segments in each age group shows that there are four segments in the age group 4-12. The rest of the age groups have more segments. This age group watches 16% of the films in the cinema, less than any other age group.

This question perfectly illustrates how useful the previous tip was. The information regarding the segment’s key and different movie types is irrelevant; only how many segments each age group holds matters. Starting from the question, you can save valuable time.

The correct answer is A

WorkKeys Graphic Literacy Test – Level 6 Question

You are a police officer in Ciny Town. You have just turned right from Maple St. on your way to the Police Stop Station on Laurence Rd. when you are called to attend an emergency meeting near the other police stop. Which way would you take to arrive at your destination as quickly as possible?

An arrow on a street indicates that, unless otherwise specified, along the entire street traffic is only allowed to travel in the direction in which the arrow is pointing.

Note: Police officers do not have to adhere to traffic regulations during emergencies.

A. Left on Hare St. and left on Anderson Ave.

B. Straight on Laurence Rd., left on Gale St., and left on Anderson Ave.

C. Left on Hare St., right on Smith Ln., and right on Hill St.

D. Left on Hare St. and left on Smith Ln.

E. Left on Hare St. and right on Laurence Rd.

Answer: the correct answer is A.

It is an emergency meeting, so you do not need to regard the traffic regulations.

Answer (B) is incorrect because it would take longer to arrive.

Answer (C) is incorrect because making a right turn on Smith Ln. is going in the wrong direction.

Answers (D) and (E) are incorrect because these routes do not take you to the Police Stop Station.

The correct answer is A

The graphs in the WorkKeys test often contain multiple pieces of data you'll need to cross-reference to answer a question correctly. For example, in the level 5 sample question, you may be asked for the percentage of the overall cinemagoers between the ages 21-45 who went to documentary films (8%). To best cross-reference information, you should:

Let’s see the final level of the Graphic Literature section!

WorkKeys Graphic Literacy Test – Level 7 Question

Which month reflects an increase in the monthly gross income from the prior month, with the largest drop in the monthly net income?

A. February

B. April

C. July

D. September

E. November

Answer: the correct answer is C.

Note that the monthly gross income increases from June to July, while at the same time, the monthly net income decreases from 6000$ to 1800$. This is the largest drop in the monthly income in the presented plot. Therefore, we can see that July has the largest drop in the monthly net income among the months, with an increased gross income from the prior month.

The correct answer is C

How could I better perform in Graphic Literacy questions?

We have one more WorkKeys practice test coming ahead – the Workplace Documents. This section is similar to the previous section as you are required to gather information from presented data; however, this time, the data is shown as a text-written document.

WorkKeys Practice Exam — Workplace Documents Sample Questions

The WorkKeys Workplace Documents section has five difficulty levels, ranging from 3 to 7.

You will have 55 minutes to answer 35 questions.

WorkKeys Workplace Documents Test – Level 3 Question

Safety Guidelines for Warehouse Workers

All warehouse workers must always wear safety gear. This includes:

Equipment such as forklifts should only be operated by certified personnel. Ensure that walkways are clear of objects to avoid trip hazards.

Based on the document, which of the following statements is correct?

A. All workers are required to operate forklifts.

B. Safety goggles are optional for warehouse workers.

C. High-visibility vests are only required for certified personnel.

D. Walkways should be clear to prevent tripping.

E. Hard hats are only required for certified personnel.

Answer : the correct answer is D.

Let’s review each answer:

Answer (A) is incorrect since it is clearly stated that: “Equipment such as forklifts should only be operated by certified personnel.”

Answer (B) is incorrect since it is included in the safety gear list.

Answers (C) and (E) are incorrect since they are also included in the safety gear list, which is mandatory for all warehouse workers.

Answer (D) is the only answer that is clearly stated: “Ensure that walkways are clear of objects to avoid trip hazards.”

The correct answer is D

WorkKeys Workplace Documents Test – Level 4 Question

Office Printer Usage Policy

Employees are permitted to use office printers for business-related tasks only. Personal printing is prohibited. Color printing should be kept to a minimum to conserve ink. Requests for specialized printing projects, such as booklets or presentations, must be approved by the IT department in advance. If the printer is out of paper, notify the administrative assistant immediately.

Based on the document, which of the following statements is correct?

A. Employees are not allowed to use office printers.

B. Personal printing is allowed for specialized projects.

C. Color printing should be avoided whenever possible.

D. IT department approval is needed for all printing tasks.

E. If the printer is out of paper, employees should refill it themselves.

Answer: the correct answer is C.

Let’s review each answer:

Answer (A): The document clearly states that employees can use office printers only for business-related tasks. Therefore, the statement "Employees are not allowed to use office printers" is incorrect.

Answer (B): The document states that personal printing is prohibited, making this statement incorrect. It also says that the IT department must approve specialized printing projects, but it does not specify that personal printing is allowed for these specialized projects.

Answer (D): According to the document, IT department approval is only required for "specialized printing projects, such as booklets or presentations." It is not needed for all printing tasks, making this statement incorrect.

Answer (E): The document instructs employees to "notify the administrative assistant immediately" if the printer is out of paper. It doesn't say employees should refill the paper themselves, making this statement incorrect.

Answer (C): The document states that "Color printing should be kept to a minimum to conserve ink," which means it should be avoided when possible.

The correct answer is C

Even if the text is as short as this one, you still must read the question first! There’s a lot of “useless” data in the text which does not refer to the question. By reading the question first, you quickly scan the text for the needed data. In the previous two questions, you were looking for the correct answer, and therefore, you should look for keywords in each answer to either eliminate it or verify it as the correct one. In other questions, you may be asked about specific information and should look for it.

WorkKeys Workplace Documents Test – Level 5 Question

Detailed Company's Annual Leave Policy

Welcome to our annual leave policy guide. The purpose of this document is to clarify our annual leave policies so that every employee can enjoy time off work while minimizing disruption to company operations. Employees are eligible for annual leave based on their years of service with the company. Understanding your leave options can help you plan your time more effectively.

Annual leave accrues according to the following rate based on your years of service:

For employees with 0-2 years of service, the annual leave accumulation rate is 10 days per year.
For those with 3-5 years of service, the accumulation rate increases to 15 days per year.
And finally, for those with more than 6 years of service, the accumulation rate is 20 days per year.
Requesting Leave

Leave must be requested at least two weeks in advance through our internal system. All leave requests are subject to managerial approval. We encourage you to coordinate with your team to ensure smooth operations during your absence.

Please be advised that annual leave cannot be taken during peak business periods, which are generally November and December, due to high project volume. Exceptions may be made but must be explicitly approved by senior management.

If you have any unused leave at the end of the calendar year, you may carry it over to the next year. However, the total accumulation of carried-over and newly accrued leave cannot exceed 30 days. Any days exceeding this limit will be automatically forfeited at the end of the calendar year.

Jane, an employee with four years of service, has eight days of unused leave at the end of the year. According to the policy, what is the maximum number of days Jane can accumulate by the end of next year?

A. 18 days

B. 23 days

C. 30 days

D. 15 days

E. 25 days

Answer: the correct answer is B.

Let’s review each answer:

Answer (A): 18 days would apply if Jane were in her first two years of employment. However, she has four years of service and falls into the "3-5 years" category.

Answer (C): Although the policy states that the maximum accumulation of carried-over and newly accrued leave cannot exceed 30 days, Jane would only reach 23 days based on her current situation.

Answer (D): 15 days is the annual leave Jane would earn in the new year, but does not consider the eight days she already has.

Answer (E): 25 days would be incorrect as Jane could accumulate up to 23 days (15 newly accrued + 8 carried over).

Answer (C): Jane falls into the "3-5 years" category, which means she accumulates 15 days of annual leave per year. Adding her 8 days of unused leave that will carry over to next year, she could accumulate 15 (newly accrued) + 8 (carried over) = 23 days by the end of the year.

The correct answer is B

WorkKeys Workplace Documents Test – Level 6 Question

Ohio State Law
Riding on roadways and bicycle paths

A. Any person operating a bicycle shall obey the instructions of official traffic-control regulations, signals, signs, and other control devices applicable to vehicles, unless directed otherwise by a police officer. Whenever authorized signs indicating that no right or left is permitted are present, no person operating a bicycle shall disobey the direction of any such sign. Such a person shall dismount from the bicycle to make any such turn and obey the regulations applicable to pedestrians.

B. Every person operating a bicycle when riding upon a roadway shall further avoid making any right, left, or U-turn except:

• When the road is completely clear of vehicles.
• When the rider of the bicycle is given the right of way from any approaching vehicles via a clearly visible signal, such as blinking of lights.
• When such a turn is necessary to avoid risk and potential danger.

C. Every person operating a bicycle upon a roadway shall ride as near the right-hand side of the road as practicable, except:

• When moving at the same speed as traffic.
• When preparing for a left turn at an intersection or into a private road or driveway.
• When reasonably necessary to avoid hazardous conditions (including, but not limited to, fixed or moving objects, vehicles, bicycles, pedestrians, animals, surface hazards, or narrow-width lanes) that make it unsafe to continue along the right-hand curb or edge.
• When approaching a location where there is a reasonable probability that a motor vehicle may turn right, crossing the bicycle's path.

When is it permissible to make a right-hand turn while staying on the bicycle?

A. It is not permissible under any circumstances.

B. It is permissible when moving at the same speed as traffic and staying near the right-hand side of the road.

C. It is permissible when the rider is turning into a private residence.

D. It is not permissible when there is light traffic and no danger to the rider.

E. It is permissible when the road ahead is too narrow to allow bicycles to ride safely.

Answer : the correct answer is B.

Answer (A) is incorrect because there are several conditions under which a right turn is permissible, as stipulated in the passage.

Answer (B) is incorrect because the conditions detailed in it are taken from a part of the law dictating the side of the road a cyclist must drive on.

Answer (C) is, once again, an exception to the rule regarding riding on the right side of the road. It is not one of the conditions for making a right turn.

Answer (D) is incorrect because a right-hand turn is allowed when there is either no traffic or immediate danger. The strong wording excludes light traffic: "When the road is completely clear of vehicles".

Answer (E) describes a situation in which a right turn is necessary to avoid the danger of riding alongside fast cars on a road that is not wide enough for it. Avoidance of risk or danger is the last out of three conditions under which the Law allows cyclists to make a turn while mounted on their bike.

The correct answer is B

As the first tip in this WorkKeys Free Test – use the tools you are provided. This time, we are referring to the scratchpad. When approaching long texts, you should summarize important parts in bullets, short sentences, or any other way you prefer. This way, you create faster, easier-to-manipulate pieces of information for you to use since the answers now require processing of the text. We also recommend using the highlighter – mark important sentences or keywords in the text to return to.

Let’s move on to the final question of the Workplace Document section.

WorkKeys Workplace Documents Test – Level 7 Question

ICC IBC High-Rise Constriction Regulations

403.2.3 Structural integrity of exit enclosures and elevator hoistway enclosures. For high-rise buildings of occupancy category III or IV in accordance with the previous section, and for all buildings that are more than 420 feet (128 m) in building height, exit enclosures and elevator hoistway enclosures shall comply with Sections 403.2.3.1 through 403.2.3.4.

403.2.3.1 Wall assembly. The wall assemblies making up the exit enclosures and elevator hoistway enclosures shall meet or exceed Soft Body Impact Classification 2009 Level 2 as measured by the test method described in ASTM C 1629/C.

403.2.3.2 Wall assembly materials. The wall assemblies making up the exit enclosures and elevator hoistway enclosures, for all floors of the building starting from the first floor and including all floors constructed underground, shall be constructed in accordance with one of the following methods:

The wall assembly shall incorporate no less than two layers of impact-resistant construction board each of which meets or exceeds Hard Body Impact Classification Level 2 as measured by the test method described in ASTM C 1629/C.
The wall assembly shall incorporate no less than one layer of impact-resistant cement that meets or exceeds Hard Body Impact Classification Level 3 as measured by the test method described in ASTM C 1629/C.
The wall assembly incorporates multiple layers of any material, tested in tandem, that meet or exceed Structural Impact Classification Level H as measured by the test method described in ASTM C 1629/C.
The exterior of a wall assembly making up the exit enclosure and elevator hoistway enclosure, regardless of the material used, must meet or exceed Soft Body Impact Classification 2009 Level 3 as measured by the test method described in ASTM C 1629/C. If the exterior is made of glass, metal, or wood, the exterior must meet or exceed Soft Body Impact Classification 2009 Level 5.
403.2.3.3 Concrete and masonry walls. Concrete or masonry walls shall be deemed to satisfy the requirements of Sections 403.2.3.1 and 403.2.3.2. 403.2.3.4. Other wall assemblies. Any other wall assembly that provides impact resistance equivalent to that required by Sections 403.2.3.1 and 403.2.3.2 for Hard Body Impact Classification Level 3, as measured by the test method described in ASTM C 1629/C, shall be permitted.

An engineer declared a newly constructed high-rise building to be in violation of the ICC IBC. Which of the following could not be the reason?

A. The wall making up the exit enclosure to the first floor is made from impact-resistant cement that has not been tested for Soft Body Impact

B. The wall assembly for the elevator shaft is made of one layer of impact-resistant construction board that tested and exceeded the Hard Body Classification Level 2

C. The wall assembly for the exit enclosure is made of multiple layers of reinforced geopolymer boards that were tested separately and exceeded the Structural Impact Classification Level H

D. The wall assembly for the elevator shaft is a two-layer masonry wall whose layers were tested together and exceeded the Structural Impact Classification Level H

E. The wall assembly for the elevator shaft is a single-layer concrete wall that tested and exceeded the Hard Body Impact Classification Level 2

Answer: the correct answer is D.

Let’s review each answer:

Answer (A) is incorrect because the wall in it has not been tested in the required test (Soft Body Impact).

Answer (B) is incorrect because if a wall is made of impact-resistant construction board, the regulations require two layers.

Answer (C) is incorrect because the cement boards in it were tested separately, while the regulations require the test to be done “in tandem” (meaning together or simultaneously).

Answer (E) is incorrect because a concrete wall, like masonry, must have multiple layers and pass a Hard Body Impact Classification Level 3 test, not Level 2.

Answer (D) This is the only answer that does not violate the ICC IBC regulations. Masonry walls must fill the requirements of “multiple layers of any material,” meaning they must meet or exceed a Hard Body Impact Classification Level 3 test.

The correct answer is D

Now that we have finished covering the most common sections of the ACT WorkKeys, which align with the requirement of receiving the National Career Readiness Certificate, we will move on to additional sections, which may or may not appear in your test – according to the requirements of your position. These sections cover mechanical knowledge, writing abilities, and personality traits.

We will begin this part of the WorkKeys Assessment Practice Test with Applied Technology – a section that assesses your physical knowledge, both in concept and practice. It may include electricity, fluid dynamics, mechanics, and thermodynamics.

WorkKeys Practice Exam — Applied Technology Sample Questions

The WorkKeys Applied Technology section has three-four difficulty levels, ranging from 3 to 5/6.

You will have 55 minutes to answer 34 questions.

WorkKeys Applied Technology (Electricity) Test – Level 3 Question

In the circuit below, how many bulbs would light up if switch I were closed, and switch II was open?

A. One

B. Two

C. Three

D. Four

E. None

Answer : the correct answer is C.

If you close switch I and leave switch II open (see the red line in the drawing), you can see that bulbs c, b, and a are still sitting on a closed circuit containing the battery.

The branch containing bulb d is disconnected from the circuit, causing zero current to flow through it, and thus this bulb does not light up. Without it, only three bulbs would light up.

The correct answer is C