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题库 / Prep2012-CR-34
In polluted environments, dolphins gradually accumulate toxins in their body fat, and the larger the dolphin the more accumulated toxins it can tolerate. Nearly 80 percent of the toxins a female dolphin has accumulated pass into the fat-rich milk her nursing calf ingests. Therefore, the unusually high mortality rate among dolphin calves in the industrially contaminated waters along Florida's Gulf Coast is probably the result of their being poisoned by their mother's milk.
Which of the following, if true, most strengthens the argument?
The survival rate of firstborn dolphin calves in the area along Florida's Gulf Coast is highest for those whose mothers were killed before they were weaned.
The rate at which adult dolphins living in the waters along Florida's Gulf Coast accumulate toxins is no higher than that of adult dolphins in comparably polluted waters elsewhere.
Among dolphin calves born in the area along Florida's Gulf Coast, the mortality rate is highest among those with living siblings.
As dolphins age, they accumulate toxins from the environment more slowly than when they were young.
Dolphins, other marine mammals, have a higher proportion of body fat than do most land mammals.
错选C，sibling--兄弟姐妹，C选项说在这个污染的地方，有兄弟姐妹的幼崽在所有幼崽中死亡率越高。这其实说明了并不是奶水造成死亡，反而是因为有兄弟姐妹造成死亡，所以是削弱。
而A选项，意思是，那些在断奶前丧母的幼崽存活率高。断奶前丧母，这表明了他们都没怎么喝奶，或者说喝奶时间比较短，所以存活率高，也就加强了喝污染奶导致死亡。
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