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.
Answers
The first thing to notice here is that we are looking for examples of neurogenesis. Because neurogenesis is an activity, a kind of growth, neither mice nor their brains can be an example of neurogenesis. We can eliminate A - C for this reason. We can eliminate D because it has a modifier error. "When placed" is an adverbial modifier, and should therefore modify an action or clause. For instance, we might say "When placed in a stimulating environment, mice grow new brain cells," or "Mice grow new brain cells when placed in a stimulating environment." All we have to modify here is a noun phrase--"the brain growth"--so we should not use an adverbial modifier. Note that we have the same modifier in A, but it is wrong for a slightly different reason. There, we have "the brain growing," which can be interpreted as an action, but now when we apply "when placed in a stimulating environment," it looks like we are saying that [i]the brain,[i] rather than the mouse, is being placed in that environment.
Note that in E, we have a noun modifier--"that are placed in a stimulating environment." This correctly modifies "mice." In turn, the phrase "in mice" correctly modifies "brain growth" to provide an example of neurogenesis. The parallel portion about canaries works in exactly the same way.
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