Over a range of frequencies from 100 to 5,000 hertz, monkeys

The only portion of the sentence that isn't underlined is "above which the sensitivity begins to differ". "Which" is a tricky word on the GMAT — it always indicates a modifier, and it always refers to the noun closest to the modifier.

Thinking about the meaning of the sentence, we should be able to determine that "which" is meant to refer to "a range of frequencies from 100 to 5,000 hertz" — while monkeys and marmosets have similar hearing sensitivity to humans over this range, ABOVE this range, the sensitivity is different. This means that in our sentence, "a range of frequencies from 100 to 5,000 hertz" must be right next to our modifier — at the end of the underlined portion.

Looking at the answer choices, we see that only B and E place "a range of frequencies from 100 to 5,000 hertz" next to the modifier, so we can eliminate all other options.

Looking closer at B, we should clue in on the first part of the sentence: "Compared to humans, the hearing sensitivity of monkeys and marmosets..." When we compare two things, those things must be similar: we can compare humans to monkeys and marmosets, and we can compare the hearing sensitivity of humans to the hearing sensitivity of monkeys and marmosets, but we can't compare humans to hearing sensitivity. It just doesn't make sense. If the sentence instead said "Compared to that of humans, the hearing sensitivity of monkeys and marmosets...", it would have worked. So we can eliminate B, leaving us with the correct answer, E.

As a final note, we could have also eliminated answers A, C, and D for parallelism reasons alone — they all compare hearing sensitivity to humans.