# Quiz 19: The Second Law of Thermodynamics

Physics & Astronomy

Q 1Q 1

A heat engine absorbs heat Q from a hot reservoir. The amount of work done by the engine
A) is Q.
B) must be greater than Q.
C) must be less than Q.
D) could be greater than Q.
E) is zero.

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Multiple Choice

C

Q 2Q 2

A heat engine exhausts heat Q to a cold reservoir. The amount of work done by the engine
A) is Q.
B) must be greater than Q.
C) must be less than Q.
D) could be greater than Q.
E) is zero.

Free

Multiple Choice

D

Q 3Q 3

The diagram below is a schematic of a heat engine. The three quantities, Q

_{H}, Q_{L}_{,}and W are represented, respectively, by A) 1, 2, 3 B) 1, 3, 2 C) 2, 3, 1 D) 3, 1, 2 E) 3, 2, 1Free

Multiple Choice

B

Q 4Q 4

A heat engine absorbs 150 J of heat from a hot reservoir and rejects 90 J to a cold reservoir. What is the efficiency of this engine?
A) 20%
B) 40%
C) 60%
D) 67%
E) 90%

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Multiple Choice

Q 5Q 5

A heat engine with an output of 300 W has an efficiency of 25% and works at 10 cycles/s. How much heat is absorbed (Q

_{h}) and how much rejected (Q_{c}) in each cycle? A) Q_{h}= 150 J, Q_{c}= 120 J B) Q_{h}= 1500 J, Q_{c}= 1200 J C) Q_{h}= 40 J, Q_{c}= 10 J D) Q_{h}= 120 J, Q_{c}= 90 J E) Q_{h}= 1200 J, Q_{c}= 900 JFree

Multiple Choice

Q 6Q 6

A heat engine absorbs 64 kcal of heat from a hot reservoir and exhausts 42 kcal to a cold reservoir each cycle. Its efficiency is
A) 30%
B) 34%
C) 38%
D) 40%
E) 42%

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Multiple Choice

Q 7Q 7

A heat engine absorbs 70 kcal of heat from a hot reservoir and exhausts 50 kcal to a cold reservoir each cycle. Its efficiency is
A) 20%
B) 24%
C) 29%
D) 33%
E) 37%

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Multiple Choice

Q 8Q 8

A substance undergoes a series of reversible processes that bring it back to its initial state. In this cycle, heat Q

_{x}is absorbed by the substance and heat Q_{y}is rejected. The net amount of work performed by the substance is A) Q_{y}- Q_{x }B) Q_{x}- Q_{y }C) (Q_{y}- Q_{x})/Q_{y }D) (Q_{x}- Q_{y})/Q_{x }E) (Q_{x}- Q_{y})/Q_{y }Free

Multiple Choice

Q 9Q 9

A heat engine operating between the temperatures T

_{1}and T_{2}takes in Q_{1}calories at temperature T_{1}and gives up Q_{2}calories at temperature T_{2}. The efficiency of this heat engine is A) (Q_{1}- Q_{2})/Q_{2 }B) (Q_{1}- Q_{2})/Q_{1 }C) (T_{2}- T_{1})/T_{2 }D) Q_{2}/(Q_{1}- Q_{2}) E) T_{1}/(T_{1}- T_{2})Free

Multiple Choice

Q 10Q 10

An engine operating in a cycle would violate the second law of thermodynamics if it
A) changed all the heat from a source to mechanical work.
B) changed all of its mechanical work to heat.
C) were irreversible.
D) operated between two isotherms and two adiabats.
E) were less efficient than a Carnot engine.

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Multiple Choice

Q 11Q 11

Use the following diagram to answer the next problems. An ideal heat engine uses 0.01 mol of gas and operates between a hot reservoir at
T

_{H}= 400 K and cold reservoir at T_{L}= 300 K, in a cycle from abcda. From ab the gas undergoes an isothermal expansion, changing its volume from V_{a}to 2.5V_{a}. From bc, the pressure is reduced at a constant volume. From cd, the gas undergoes an isothermal compression, and from da, the pressure is increased at a constant volume until the gas is back at the original condition at a. -How much work is obtained from the engine in each cycle? A) 22.9 J B) 30.5 J C) 7.62 J D) 8.31 J E) 0.917 JFree

Multiple Choice

Q 12Q 12

Use the following diagram to answer the next problems. An ideal heat engine uses 0.01 mol of gas and operates between a hot reservoir at
T

_{H}= 400 K and cold reservoir at T_{L}= 300 K, in a cycle from abcda. From ab the gas undergoes an isothermal expansion, changing its volume from V_{a}to 2.5V_{a}. From bc, the pressure is reduced at a constant volume. From cd, the gas undergoes an isothermal compression, and from da, the pressure is increased at a constant volume until the gas is back at the original condition at a. -If the engine operates at 50 cycles per second, the power output is A) 381 W B) 45.8 W C) 1145 W D) 415 W E) 1525 WFree

Multiple Choice

Q 13Q 13

Use the following diagram to answer the next problems. An ideal heat engine uses 0.01 mol of gas and operates between a hot reservoir at
T

_{H}= 400 K and cold reservoir at T_{L}= 300 K, in a cycle from abcda. From ab the gas undergoes an isothermal expansion, changing its volume from V_{a}to 2.5V_{a}. From bc, the pressure is reduced at a constant volume. From cd, the gas undergoes an isothermal compression, and from da, the pressure is increased at a constant volume until the gas is back at the original condition at a. -How much heat is absorbed in going from ab? A) 30.5 J B) 7.62 J C) 22.9 J D) 8.31 J E) 0.917 JFree

Multiple Choice

Q 14Q 14

If you run a refrigerator in a closed room with the door to the refrigerator open, the temperature of the room
A) increases.
B) remains the same.
C) decreases.
D) Any of these can happen depending on how efficient the refrigerator is.
E) Any of these can happen depending on the relative sizes of the room and the refrigerator.

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Multiple Choice

Q 15Q 15

Two refrigerators, one with a COP of 4.0 and another with a COP of 5.0, both extract 400 kJ of heat from the cold reservoir (food). Calculate the difference in energy they exhaust to the hot reservoir and hence the room.
A) 320 kJ
B) 80 kJ
C) 125 kJ
D) 100 kJ
E) 20 kJ

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Multiple Choice

Q 16Q 16

A refrigerator extracts 25 kJ from a cold reservoir and rejects 35 kJ to a hot reservoir. What is the coefficient of performance of this refrigerator?
A) 2.5
B) 3.5
C) 1.4
D) 5.0
E) 4.0

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Multiple Choice

Q 17Q 17

For which of the following is COP the abbreviation?
A) Clausius or Planck
B) cycle of pressure
C) coefficients of pressure
D) Carnot ordered performance
E) coefficient of performance

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Multiple Choice

Q 18Q 18

A refrigerator extracts heat Q from a cold reservoir. The heat exhausted to a hot reservoir
A) is Q.
B) must be greater than Q.
C) must be less than Q.
D) could be greater than Q.
E) is zero.

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Multiple Choice

Q 19Q 19

A refrigerator with a coefficient of performance 5.0 removes 25 kJ of heat from a cold reservoir. If this refrigerator is reversible and is run backward as a heat engine, what would be the efficiency of the heat engine?
A) 50%
B) 80%
C) 83%
D) 17%
E) 20%

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Multiple Choice

Q 20Q 20

A refrigerator has a coefficient of performance 5.0. How much heat is exhausted to the hot reservoir when 200 kJ of heat are removed from the cold reservoir?
A) 50 kJ
B) 150 kJ
C) 200 kJ
D) 240 kJ
E) Not enough information is given to answer this question.

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Multiple Choice

Q 21Q 21

A refrigerator has a coefficient of performance 4.0. How much heat is exhausted to the hot reservoir when 400 kJ of heat are removed from the cold reservoir?
A) 500 kJ
B) 400 kJ
C) 100 kJ
D) 80 kJ
E) Not enough information is given to answer this question.

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Multiple Choice

Q 22Q 22

You want to construct a perfect refrigerator from a perfect heat engine. What else do you need?
A) You need a second perfect heat engine.
B) You need a nonperfect heat engine.
C) You need a nonperfect refrigerator.
D) You need nothing else. A perfect refrigerator is just a perfect heat engine run backward.
E) A perfect refrigerator cannot be constructed even if you have a perfect heat engine.

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Multiple Choice

Q 23Q 23

What is the maximum possible efficiency of a steam engine operating between a high and low temperature of 550C and 180C?
A) 45%
B) 67%
C) 55%
D) 33%
E) 82%

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Multiple Choice

Q 24Q 24

If a steam engine operates at half of its theoretical maximum efficiency (e

_{max}) and does work at a rate of W J/s, calculate how much heat is discharged per second. A) W (1 e_{max}/2) / 2e_{max }B) 2W (1 e_{max}) / e_{max }C) W (1 e_{max}) / e_{max }D) W (2 2e_{max}/2) / (e_{max}/2) E) 2W (1 e_{max}/2) / e_{max }Free

Multiple Choice

Q 25Q 25

A steam engine operates between a high and low temperature of 550C and 180C. If the steam engine operates at 40% of its theoretical maximum efficiency and does work at a rate of 1000 W, calculate how much heat is discharged per hour.
A) 0.8 MJ/hr
B) 2.8 MJ/hr
C) 3.4 MJ/hr
D) 16 MJ/hr
E) 12 MJ/hr

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Multiple Choice

Q 26Q 26

We wish to increase the efficiency of an ideal heat engine from 25% to 35%. If the initial temperature of the hot reservoir is 650C, to what temperature would this need to be increased assuming the exhaust temperature remains the same?
A) 1065C
B) 910C
C) 1019C
D) 973C
E) 792C

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Multiple Choice

Q 27Q 27

The maximum theoretical thermal efficiency of a steam engine that is supplied steam at a temperature of 600ºC and exhausts it at a temperature of 200ºC is
A) 33.3%
B) 45.8%
C) 66.7%
D) 77.1%
E) 84.6%

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Multiple Choice

Q 28Q 28

A steam engine with a boiler temperature of 227ºC and an exhaust temperature of 27ºC has a maximum efficiency of approximately
A) 67%
B) 88%
C) 14%
D) 12%
E) 40%

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Multiple Choice

Q 29Q 29

The Carnot efficiency for a heat engine operating between the temperatures of 227º C and 27ºC is
A) 20%
B) 25%
C) 40%
D) 88%
E) 100%

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Multiple Choice

Q 30Q 30

A Carnot heat engine absorbs heat Q from a hot reservoir at 127ºC and exhausts heat to a cold reservoir at 27ºC. How much heat is exhausted to the cold reservoir?
A) Q
B) 27Q/127
C) 127Q/27
D) 3Q/4
E) 4Q/3

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Multiple Choice

Q 31Q 31

The schematic diagram above illustrates a Carnot engine. Which two paths of the cycle is work done by the gas?
A) 12, 23
B) 23, 34
C) 34, 41
D) 41, 12
E) only 12

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Multiple Choice

Q 32Q 32

The Carnot cycle consists of
A) a quasistatic isothermal absorption of heat from a hot reservoir.
B) a quasistatic adiabatic expansion to a lower temperature.
C) a quasistatic isothermal exhaustion of heat to a cold reservoir.
D) a quasistatic adiabatic compression to the initial state of the system.
E) All of these are correct.

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Multiple Choice

Q 33Q 33

In a nuclear power plant, heat is taken from the reactor core at 300ºC, work is done to drive an electric generator, and heat is rejected to the environment at 40ºC. What is the maximum possible thermal efficiency of this system?
A) 13%
B) 27%
C) 45%
D) 55%
E) 87%

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Multiple Choice

Q 34Q 34

The efficiency of a Carnot engine operating between 300º C and 250ºC is about
A) 83%
B) 17%
C) 57%
D) 43%
E) 9%

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Multiple Choice

Q 35Q 35

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC. How much heat is rejected to the cold reservoir in doing 1.0 kJ of work?
A) 3.8 kJ
B) 0.83 kJ
C) 2.8 kJ
D) 1.8 kJ
E) 0.67 kJ

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Multiple Choice

Q 36Q 36

A Carnot engine operating between reservoir temperatures of 340º C and 40ºC has an efficiency of
A) 37.5%
B) 49.0%
C) 60.0%
D) 62.5%
E) 88.2%

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Multiple Choice

Q 37Q 37

An electric power plant generates 100 MW of power at an efficiency of 35%. At what rate must water be circulated pass the condenser if the change in water temperature is not to exceed 10ºC?
A) 2400 kg/s
B) 6800 kg/s
C) 3400 kg/s
D) 11300 kg/s
E) 4400 kg/s

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Multiple Choice

Q 38Q 38

The construction of a heat engine operating between temperatures T

_{1}and T_{2}, and having an efficiency greater than that of a Carnot engine operating between the same two temperatures, would constitute a violation of A) the law of the conservation of energy. B) the first law of thermodynamics. C) the second law of thermodynamics. D) Boyle's law. E) None of these is correct.Free

Multiple Choice

Q 39Q 39

You can vary the efficiency of a Carnot engine by varying the temperature of the cold reservoir while maintaining the hot reservoir at constant temperature. The curve that best represents the efficiency of such an engine as a function of the temperature of the cold reservoir is
A) 1
B) 2
C) 3
D) 4
E) 5

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Multiple Choice

Q 40Q 40

Of the four steps in the Carnot cycle,
A) two are isothermal and two are isobaric.
B) two are adiabatic and two are isobaric.
C) two are isovolumic and two are isothermal.
D) two are adiabatic and two are isothermal.
E) two are adiabatic and two are isovolumic.

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Multiple Choice

Q 41Q 41

What is the maximum possible coefficient of performance of a heat pump that is capable of maintaining the interior of a house at +20ºC when the temperature outside is -40ºC?
A) 2.0
B) 5.2
C) 12
D) 4.9
E) 3.9

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Multiple Choice

Q 42Q 42

A heat pump with COP = 5 uses electrical energy W to heat a house. How much heat is pumped into the house?
A) W
B) 5W
C) 6W
D) 4W
E) 1.2W

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Multiple Choice

Q 43Q 43

An ideal heat pump is used to pump head from the outside air at -5ºC to the hot-air supply for the heating fan in a house, which is at 35ºC. How much work is required to pump
1)5 kJ of heat into the house?
A) 0.165 kJ
B) 0.195 kJ
C) 0.205 kJ
D) 0.212 kJ
E) 0.224 kJ

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Multiple Choice

Q 44Q 44

What is the maximum possible coefficient of performance of a heat pump that is capable of maintaining the interior of a house at 23ºC when the temperature outside is -30ºC?
A) 4.59
B) 3.27
C) 4.87
D) 2.63
E) 5.21

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Multiple Choice

Q 45Q 45

A heat pump needs to supply 20 kW of power to maintain the inside temperature of a house at 25C while the outside temperature is 0C. What is the power needed for the heat pump?
A) 3.36 kW
B) 2.42 kW
C) 2.78 kW
D) 4.12 kW
E) 1.68 kW

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Multiple Choice

Q 46Q 46

A heat pump needs to supply 20 kW of power to maintain the inside temperature of a house at 25C while the outside temperature is 0C. What is the savings in the electric bill per month by using the heat pump instead of direct electrical heating? Assume that the heat pump/direct heating is on for 4 hours per day and 1 kW.hr costs $0.10.
A) $220
B) $20.2
C) $200
D) $40.4
E) $80.8

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Multiple Choice

Q 47Q 47

What is the entropy change when 4 kg of water at 0C is frozen into 4 kg of ice at 0C?
A) 4.9 kJ/K
B) an infinite change
C) 4.9 kJ/K
D) 1340 kJ/K
E) 33 kJ/K

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Multiple Choice

Q 48Q 48

When you make ice cubes, the entropy of the water
A) decreases.
B) remains unchanged.
C) increases.
D) is unchanged as the water cools but decreases as the water freezes.
E) decreases while the water is cooling but does not change as it turns to ice.

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Multiple Choice

Q 49Q 49

The change in the entropy of the universe due to an operating Carnot engine
A) is zero.
B) must be positive.
C) must be negative.
D) could be positive or negative.
E) is meaningless to consider, because a Carnot engine has no connection to entropy.

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Multiple Choice

Q 50Q 50

A quantity of heat is removed from a hot reservoir at absolute temperature T and then is added to a cold reservoir at absolute temperature T/2. The cold reservoir experiences an entropy increase S. What is the change in the entropy of the universe?
A) S
B) zero
C) -S
D) 2S
E) S/2

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Multiple Choice

Q 51Q 51

A car of mass 2000 kg is traveling at 22.0 m/s on a day when the temperature is 20.0ºC. The driver steps on the brakes and stops the car. By how much does the entropy of the universe increase?
A) 1.6 kJ/K
B) 24 kJ/K
C) 4.8 10

^{5}J/K D) 0.15 kJ/K E) 3.3 kJ/KFree

Multiple Choice

Q 52Q 52

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC. What is the change in the entropy of the universe when this plant does 1.0 kJ of work?
A) 16 J/K
B) 1.7 J/K
C) 55 J/K
D) 1.7 mJ/K
E) 0.85 J/K

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Multiple Choice

Q 53Q 53

One mole of an ideal gas undergoes a reversible isothermal expansion from a volume of
1 L to a volume of 2 L. The change in entropy of the gas in terms of the universal gas constant R is
A) R/2
B) 2R
C) R ln(2)
D) R ln(½)
E) None of these is correct.

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Multiple Choice

Q 54Q 54

A thermodynamic system is taken in equilibrium steps from State I to State II. The quantities by which the process can be characterized are
1 internal energy,
2 entropy,
3 temperature,
4 work, and
5 heat.
Of these quantities, those that are independent of path are
A) 1, 2, and 3.
B) 2, 3, and 4.
C) 3, 4, and 5.
D) 1, 3, and 5.
E) 2, 3, and 5.

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Multiple Choice

Q 55Q 55

Two moles of a gas at T = 350 K expand quasistatically and isothermally from an initial volume of 20 L to a final volume of 60 L. The change in entropy of the gas during this expansion is (R = 8.314 J/mol·K)
A) -17.4 J/K
B) 18.3 J/K
C) 20.4 J/K
D) -24.6 J/K
E) 27.8 J/K

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Multiple Choice

Q 56Q 56

Three moles of a gas at T = 250 K expand quasi-statically and adiabatically from an initial volume of 30 L to a final volume of 60 L. The change in entropy of the gas during this expansion is (R = 8.314 J/mol·K)
A) 17.3 J/K
B) 18.6 J/K
C) -17.4 J/K
D) 19.5 J/K
E) zero

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Multiple Choice

Q 57Q 57

A container has 0.2 mole of O

_{2}gas and the gas is heated from 0C to 100C. What is the change in entropy of the gas? (R = 8.314 J/mol·K) A) 1.82 J/K B) 1.30 J/K C) 0.78 J/K D) 26.8 J/K E) zeroFree

Multiple Choice

Q 58Q 58

A block of mass m = 0.2 kg slides across a rough horizontal surface with coefficient of kinetic friction

_{k}= 0.5. What is the change in entropy after the block has moved a distance of 1 m? The temperature of the block and surrounding is 22C. A) 4.510^{ }^{2}J/K B) 3.310^{ }^{3}J/K C) 6.710^{ }^{3}J/K D) 9.010^{ }^{3}J/K E) zeroFree

Multiple Choice

Q 59Q 59

Entropy is related to probability. An isolated system moves toward
A) a highly ordered state of low probability and high entropy.
B) a highly ordered state of high probability and high entropy.
C) a state of low order, high probability, and high entropy.
D) a state of low order, low probability, and high entropy.
E) a state of low order, high probability, and low entropy.

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Multiple Choice

Q 60Q 60

Which of the following statements is true of an isolated system consisting of 15 gas molecules?
A) According to the second law, the entropy of the gas cannot decrease.
B) According to the second law, the entropy of the gas cannot increase.
C) According to the second law, the entropy of the gas is not likely to decrease.
D) According to the second law, the entropy of the gas is not likely to increase.
E) According to the second law, the entropy of the gas must stay the same.

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Multiple Choice

Q 61Q 61

A box contains 10 red and 10 white marbles. The box is then given a good shake. What is the probability that all the 10 red marbles will be at the bottom of the box?
A) 1/1024
B) 1/2048
C) 1/512
D) 1/2
E) zero

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Multiple Choice