Animals whose natural habitats are endangered by industrial developmen

VERITAS PREP OFFICIAL SOLUTION:

This problem deals with a number of decision points, most notably the "either X or Y" construction that begs two things: 1) the word "or" to go with "either" (this eliminates choice E), and 2) a parallel construction between the portion after "either" and the portion after "or."

Note that the word after "either" is "migrate," a present verb parallel to "try." Since "trying" changes the tense and is not parallel, you can eliminate choice B.

For strict parallel structure standards, note what happens in correct answer choice D. If you simply break the construction into the verbs, you have "Animals either migrate, leading to X, or try, often leading to Y." That participial phrase "leading" is parallel as the modifier for both parallel verbs, making a perfectly parallel construction and rendering choice D correct.

You can also eliminate choice A given the restrictive "which" modifier. It's not "environments" leading to potential ecological imbalances, and even if you didn't see that logically the verb "leads" is singular and "environments" is plural, meaning that the construction fails there, too. Finally, in choice C a logical flaw takes place: "and can lead" would mean that "lead" is parallel to "migrate." That would mean that it is the animals that can lead to imbalances, when logically it is the situation caused by their mass migration.