Here's the
official explanation provided by the GMAC for this question:
The sentence mentions a group of people who left one area and moved to another. The original version says that they
were forced to withdraw to one area from the other. In the absence of any overriding reason to mention the destination first, it is more standard and direct to mention the people’s earlier location before their later location: they went from point A to point B. In this sentence there is no plausible reason to mention the environmental changes except to indicate that they caused the relocation, so the verb forms and sentence structure should make this causal connection clear.
Option A: Saying that the people were forced to
withdraw to one location
from another location is less clear, direct, and idiomatically standard than mentioning the
from location before the
to location.
Option B: The verb form
had been forced seems to indicate that when the environmental changes took place, the people had already relocated and that the cause of their relocation was some unspecified earlier event. That makes the author’s purpose in mentioning the environmental changes unclear and their relationship to the relocation puzzling.
Option C: Correct. This wording is clear, concise, and direct, and the verb forms clearly express a coherent causal sequence of events.
Option D: This is awkward and indirect. The verb form
having been forced and the comma before
withdrew suggest that the people had already been forced before the environmental changes took place. They also make it unclear whether the people were forced by the environmental changes or by some unmentioned factor. With no comma after
inhabitants to bracket the phrase
having been forced to, there is no grammatical subject for
withdrew.Option E: This is awkward, verbose, and indirect. Setting off the phrase
because they were forced to parenthetically between commas makes it unclear whether the people were forced to withdraw by the environmental changes by or some unmentioned factor.
The correct answer is C.
Please note that I'm not the author of this explanation. I'm just posting it here since I believe it can help the community.
_________________