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  3. Because adult iguanas on Plazos Island are much smaller than adult iguanas of th

Because adult iguanas on Plazos Island are much smaller than adult iguanas of th

游客2025-02-26  13
问题 Because adult iguanas on Plazos Island are much smaller than adult iguanas of the same species on nearby islands, researchers assumed that environmental conditions on Plazos favor the survival of relatively smaller baby iguanas(hatchlings)in each yearly brood. They discovered instead that for each of the past three years, 10 percent of the smaller and 40 percent of the larger hatchlings survived, because larger hatchlings successfully evade their predators. Which of the following, if true about Plazas but not about nearby islands, contributes most to an explanation of the long-standing tendency of iguanas on Plazos to be smaller than those of the same age on nearby islands?
选项 A、Periodic wind shifts cause extended dry spells on Plazos every year, putting the larger iguanas, whose bodies require relatively more water, at a great disadvantage.
B、There are exactly three species of iguanas on Plazos but only two species of seagulls that feed on iguanas, and a relatively small percentage of each year’s hatchlings are consumed by seagulls.
C、Wild cats, which were introduced as pets by early settlers and which were formerly major predators of Plazos iguanas, were recently killed off by a disease specific to cats.
D、The iguanas on Plazos are a relatively ancient part of the island’s animal life.
E、Both land and marine iguanas live on Plazos, and the land iguanas tend to be larger than marine iguanas of the same age.
答案 A
解析 本题问题目的为解释两者差异，重点抓住差异点——本题中为“小”，并用之定位，在5个选项中涉及“大、小”概念的只有(A)与(E)两个选项。而(A)指出由于气候原因，Plazos岛上的大蜥蜴生存条件恶化，再加上问题目的中的“if true about plazos but not about nearby islands”，所以(A)正确，(E)只说明陆地蜥蜴比海洋蜥蜴大，却不能说明为什么比其他岛上的蜥蜴小。
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