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题库 / Prep2007E1-CR-3
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?
It is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.
Prairie vole populations vary dramatically in size from year to year.
The prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.
Winters in the prairie voles' habitat are often harsh, with temperatures that drop well below freezing.
Snakes, a major predator of young prairie voles, are active only from spring through early autumn.
果因，族群规模季节性变化是因为死亡率。规模大：秋冬；小：春至秋
加强，结果：季节性变化
寻找选项中有他因影响的
A、春到早夏，时间定位不对；幼崽多与死亡率无关 NM
B、每年，时间定位不对
C、春季，时间定位不对；阔叶林与死亡率无关 NM
D、冬天，时间定位不对；冷，可以说明死亡率，但不能解释族群规模大小
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