LSAT Explanation PT 25, S4, Q15: The southern half of a certain

LSAT Question Stem

If the statements in the passage are true, each of the following could be true EXCEPT: 

Logical Reasoning Question Type

This is a Must Be False question. 

Correct Answer

The correct answer to this question is E. 

LSAT Question Complete Explanation

This LSAT problem presents us with an "except" question, which means we are looking for the one answer choice that could NOT be true given the information provided in the passage. Let's briefly review the passage and then analyze each answer choice.

The passage tells us that during the Cretaceous period, the southern half of a certain region was entirely covered by water. Dinosaurs lived only on land, and no single species of dinosaur lived throughout the entire Mesozoic era. Plesiosaurs, swimming reptiles, lived during the Cretaceous period exclusively and were not dinosaurs.

Now let's evaluate each answer choice:

a) Dinosaurs inhabited the northern half of the region throughout the entire Mesozoic era.

This answer choice could be true. Even though no single species of dinosaur lived throughout the entire Mesozoic era, different species could have inhabited the northern half of the region at different times, collectively spanning the entire era.

b) Plesiosaurs did not inhabit the southern half of the region during the Cretaceous period.

This answer choice could also be true. The passage only tells us that plesiosaurs lived during the Cretaceous period exclusively, but it does not specify where they lived. It is possible that they lived in other aquatic areas.

c) Plesiosaurs did not inhabit the southern half of the region before the Cretaceous period.

This answer choice must be true. Since plesiosaurs lived exclusively during the Cretaceous period, they could not have inhabited the southern half of the region or any other region before the Cretaceous period.

d) Dinosaurs did not inhabit the northern half of the region during the Cretaceous period.

This answer choice could be true. The passage does not provide any information about the northern half of the region during the Cretaceous period. It is possible that dinosaurs did not inhabit this area during that time.

e) Dinosaurs inhabited the southern half of the region throughout the entire Mesozoic era.

This answer choice cannot be true, making it the correct answer. The passage tells us that the southern half of the region was covered entirely by water during the Cretaceous period, which is part of the Mesozoic era. Since dinosaurs lived only on land, they could not have inhabited the southern half of the region throughout the entire Mesozoic era.

In conclusion, the correct answer is E because it is the only answer choice that cannot be true based on the information provided in the passage.