souvonik2k
Amphibians have been able to maintain a specific level of hydration in and out of water ever since they developed neurohypophysial hormones
which adjusted the permeability of their skin.
A) which adjusted
B) that adjusts
C) which has adjusted
D) that has been adjusting
E) having adjusted
Source-Gmatfree
OFFICIAL EXPLANATION:
Creating a filter: We read the prompt, ignoring the "neuro-" word for now. The sentence passes the subject-verb test and doesn't raise flags. We proceed to the answer choices to proceed exhaustively and eliminate choices based on objective defects.
Finding objective defects: Choice (B) has a grammatically singular verb, so it's out. Same with (C) and (D). We are referring to the grammatically plural "hormones."
So we are down to (A) and (E). Choice (E) sounds weird and is flawed. When a clause is used to define or describe a noun, it should begin with the relative pronouns "which" or "that."
The correct answer is (A).