Can you answer this by reading only the first 3 words of each answer choice?
Recently documented examples of neurogenesis, the production of new brain cells, include the brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that learn new songs.
A. the brain growing in mice when placed in a stimulating environment or neurons increasing in canaries that
B. mice whose brains grow when they are placed in a stimulating environment or canaries whose neurons increase when they
C. mice's brains that grow when they are placed in a stimulating environment or canaries' neurons that increase when they
D. the brain growth in mice when placed in a stimulating environment or the increase in canaries' neurons when they
E. brain growth in mice that are placed in a stimulating environment or an increase in neurons in canaries that
Here the answer is E. Let me show you how.
This is a split sentence. Basically in the form of [main sentence, description, main sentence]
Just take out the description in the middle and read it like this:
Recently documented examples of neurogenesis include [A] or .
From this alone, you should be able to eliminate (A), (B), and (C) just be reading the first three words of each answer choice.
(A): the brain growing
(B): mice whose brains
(C): mice's brains
None of these work because they are not structured correctly as examples.
(D) and (E) are closer to what we want--either "the brain growth" or "brain growth"
The only difference between (D) and (E) is "when placed" versus "that."
"When placed" seems to suggest a more specific condition whereas "that" seems more general and a description of a state of being--more of what we're looking for.
Also, if you were to guess--choose the shorter answer choice--the one with fewer words---that would be (E).
Either way, the one you want here is (E) because it correctly begins with "brain growth in mice"--which is an example of a documented example of neurogenesis. And it's consistent with the second part of the sentence.
Therefore, the answer is (E).