LSAT Explanation PT 19, S2, Q19: When an ordinary piece of steel

LSAT Question Stem

Which one of the following most logically completes the argument? 

Logical Reasoning Question Type

This is a Must Be True question. 

Correct Answer

The correct answer to this question is E. 

LSAT Question Complete Explanation

In the passage, we learn that when steel is put under pressure, it compresses, meaning its volume slightly decreases. Glass, on the other hand, is a fluid, so when it is put under pressure, it flows rather than compressing, and its volume remains unchanged. When a heavy object is placed in the middle of a horizontal sheet of glass of uniform thickness, and the glass is able to support the weight without cracking, the glass will flow to areas under less pressure. The question type is a Must Be True (MBT) question, asking us to find the answer choice that most logically completes the argument.

Let's analyze each answer choice:

a) become larger in size yet still be of uniform thickness

This answer choice is incorrect because there is no evidence to suggest that the entire sheet of glass will maintain the same thickness everywhere. The glass will get thinner at the center due to the heavy object, but it could get thicker just beyond the area where the heavy object is sitting. The passage states that the glass flows to areas under less pressure, which means less flow and less change in those areas. Uniform thickness is not supported by the passage.

b) flow toward the point at which the pressure of the object is greatest

This answer choice contradicts the passage, which states that the glass flows to areas under less pressure, not toward the point of greatest pressure.

c) compress, although not as much as a piece of steel would

This answer choice is unsupported because the passage specifically states that glass does not compress, but rather flows when put under pressure.

d) divide into exactly two pieces that are equal in neither size nor shape to the original piece of glass

This answer choice is incorrect because it contradicts the passage. The passage states that the glass will be able to support the heavy object without cracking, so it won't split in half; it will stay as one piece.

e) be thinner in the portion of the glass that is under the pressure of the object than in those portions of the glass that are not under that pressure

This is the correct answer. Since the glass flows away from the pressure created by the heavy object, the portion under the heavy object will become thinner. The overall volume of the glass remains unchanged during this process, as stated in the passage.

I hope this explanation helps you understand the passage and the reasoning behind the correct answer choice, E.