题目信息
Modern-day snakes are believed to evolve from four-legged lizards, but scientists were divided over whether that phase of evolution occurred on land or in the sea; the recent discovery of fossils of a land-dwelling snake with two legs provides new information for the ongoing debate.
A:evolve from four-legged lizards, but scientists were
B:have evolved from four-legged lizards, but scientists are
C:evolve from four-legged lizards, but scientists are
D:have evolved from four-legged lizards, but scientists were
E:be evolving from four-legged lizards, but scientists were
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共享解析来源为网络权威资源、GMAT高分考生等； 如有疑问，欢迎在评论区提问与讨论
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正确答案：
B:have evolved from four-legged lizards, but scientists are
考察时态，用完成时更好。完成时是过去的动作或状态一直持续到现在，或者一件事发生在过去但现在仍然起作用或是事实。
蛇从四个脚的蜥蜴进化来，事情发生在过去，但是现在这件事仍然是事实。
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