The author implies which of the following about the fact that turtles, whales, and dugongs all have flippers?
答案选的B，我想问A错在哪？虽然B选项正确可以由“may indeed be a necessary response to aquatic life”推出，但那段话紧接着说“But the common detailed design found among the pinnipeds probably indicates a common ancestor”,这里的common ancestor 等同于 very closely related 吗？以及 indicates a common ancestor 与“can be explained by a common ancestor”是不是其实逻辑是上有差别？
(A) It can be explained by the hypothesis that turtles, whales, and dugongs are very closely related.
(B) It can be explained by the idea of convergent evolution.
附上我原文中的答案定位：
Flippers may indeed be a necessary response to aquatic life; turtles, whales, and dugongs also have them. But the common detailed design found among the pinnipeds probably indicates a common ancestor.
附上完整原文：Biologists have long maintained that two groups of pinnipeds, sea lions and walruses, are descended from a terrestrial bearlike animal, whereas the remaining group, seals, shares an ancestor with weasels. But the recent discovery of detailed similarities in the skeletal structure of the flippers in all three groups undermines the attempt to explain away superficial resemblance as due to convergent evolution—the independent development of similarities between unrelated groups in response to similar environmental pressures. Flippers may indeed be a necessary response to aquatic life; turtles, whales, and dugongs also have them. But the common detailed design found among the pinnipeds probably indicates a common ancestor. Moreover,walruses and seals drive themselves through the water with thrusts of their hind flippers, but sea lions use their front flippers. If anatomical similarity in the flippers resulted from similar environmental pressures, as posited by the convergent evolution theory, one would expect walruses and seals, but not seals and sea lions, to have similar flippers.