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 5 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 develop-ment of similarities between unrelated groups in 10 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,15 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 20 would expect walruses and seals, but not seals and sea lions, to have similar flippers.(162 words)
1. 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 bearlike 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.
2. 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.
3. Select the sentence in the passage in which the author shows that the implication of the common view is contradicted by a new finding.
答案：C/ B /But the common detailed design found among the pinnipeds probably indicates a common ancestor
