求问OG17-CR607

林晃晃

OG2017-607
Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils that are much older than the earliest birdlike dinosaur fossils that have been found.
Which of the following is an assumption on which the argument relies?
(A) The birdlike dinosaurs have no living descendants.
(B) There are no flightless dinosaur species that have the distinctive structural features shared by birds and birdlike dinosaurs.
(C) There are no birdlike dinosaur fossils that are older than the bird fossils but have not yet been unearthed.
(D) It could not have been the case that some birds were descended from one of the birdlike dinosaur species and other birds from another.
(E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.






答案是选C的，我能理解，但D一直想不明白为什么不可以，D说没案例说一些鸟发源于某种恐龙，另一些鸟发源于其他恐龙，鸟都是同宗的，限定了这样的假设就不会有可能出现：这些发现的鸟化石是更早的恐龙发源来的，而后面的鸟是后面的恐龙进化的，这样不是刚好支持了结论么？
OG的解释我也有点不理解。D的解释是这样的：The argument purports to establish that the relative ages of bird fossils and birdlike dinosaur fossils show that birds cannot be descended from any of the known birdlike dinosaur species. In doing this, it acknowledges multiple birdlike dinosaur species and leaves open the question of whether some birds may be descended from one such species and other birds from another such species.
新手求赐教，谢谢谢谢！

林晃晃

自己顶一下！

Bradz

d的问题是“could”。推翻d的假设，也只能说鸟的祖先could be恐龙和鸟，但也有可能could be只有鸟，也could be只有恐龙，不能够完全推翻作者鸟不能源于恐龙的论断。

林晃晃

Bradz 发表于 2016-10-19 20:27
d的问题是“could”。推翻d的假设，也只能说鸟的祖先could be恐龙和鸟，但也有可能could be只有鸟，也could ...

啊明白了！谢谢！