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Biologists have long maintained that two groups of pinnipeds, sea lions and walruses, are descended from a terrestrial bear like 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.

According to the passage, it has been recently discovered that
A.there are detailed skeletal similarities in the flippers of pinnipeds
B.sea lions, seals, and walruses are all pinnipeds
C.pinnipeds are descended from animals that once lived on land
D.animals without common ancestors sometimes evolve in similar ways
E.animals that have flippers do not all use them in the same way

The author implies that which of the following was part of the long-standing view concerning pinnipeds?
A.Pinnipeds are all descended from a terrestrial bear like animal.
B.Pinnipeds share a common ancestor with turtles, whales, and dugongs.
C.Similarities among pinnipeds are due to their all having had to adapt to aquatic life.
D.There are detailed similarities in the skeletal structure of the flippers in all pinnipeds.
E.Convergent evolution cannot account for the similarities among pinnipeds.

The author implies which of the following about the fact that turtles, whales, and dugongs all have flippers?
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.
C.It suggests that turtles, whales, and dugongs evolved in separate parts of the world.
D.It undermines the view that turtles, whales, and dugongs are all descended from terrestrial ancestors.
E.It is the primary difference between turtles, whales, and dugongs, on the one hand, and pinnipeds, on the other.

In presenting the argument in the passage, the author does which of the following?
A.Contends that key terms in an opposing view have been improperly used.
B.Contends that opponents have purposely obscured important evidence.
C.Shows that two theories thought to be in conflict are actually complementary.
D.Shows that advocates of a theory have not always stated their view in the same manner.
E.Shows that an implication of a theory is contradicted by the facts.

参考答案

正确答案:A C B E