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The prairie vole, a small North American grassland rodent, breeds year-round, and a group of voles living together consists primarily of an extended family, often including two or more litters. Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups. The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.

Which of the following, if true, provides the strongest support for the explanation offered?


Option A:

It is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.

Option B:

Prairie vole populations vary dramatically in size from year to year.

Option C:

The prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.

Option D:

Winters in the prairie voles’ habitat are often harsh, with temperatures that drop well below freezing.

Option E:

Snakes, a major predator of young prairie voles, are active only from spring through early autumn.

Difficulty Level



Option E is the correct answer.

Option Analysis

Question type: Strengthen the argument.  

Summary of the argument: The argument says that the seasonal variation in the group size of the voles is also linked to the seasonal variation in mortality among groups.  

A) The option uses proportion while the argument is concerned about actual numbers.  

B) The argument talks about the number of voles in a group and not about the general population of the voles.  

C) This doesn’t explain why the number of voles increases or decreases with seasons.  

D) Same as C. Doesn’t talk about the effect that this has on the number of voles in a group.  

E) Correct Answer