In polluted environments, dolphins gradually accumulated toxins in their body fat, and the larger the dolphin the more accumulated toxin 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.
E. Dolphins, like other marine mammals, have a higher proportion of body fat than do most land mammals. 答案是A, 可是我一点思路也没有,谁能帮我解释一下A选项,并给一个推理关系呀 先谢 | 
