GWD 一题求解 （be thought to have done）

巧克力酱

All Y chromosomes in existence today are descended from a single ancestor's who is thought to have lived about 140,000 years ago.
Aa single ancestor's who is thought to have lived  
Ba single ancestor's who was thought to live  
Ca single ancestor whom it is thought had lived  
Dthe Y chromosome of a single ancestor who is thought to have lived  
Ethe Y chromosome of a single ancestor whom it was thought had lived  

正确答案是D

我就想问问为什么这里是be thought to have lived? 后面是140,000 years ago,并不需要用完成时态呀~
求大神指点。

巧克力酱

guoyilin2015 发表于 2015-9-26 12:46
个人观点：
不定式完成时表示该动作发生在谓语动词之前。
就是说这个结构表示：它们先live，然后有人think ...

原来如此！ 谢谢啦~~~~

guoyilin2015

个人观点：
不定式完成时表示该动作发生在谓语动词之前。
就是说这个结构表示：它们先live，然后有人think。
把is thought/known/believed/claimed to have done直接砍成过去式did即可，不影响理解。
那么这句可以写成：
All Y chromosomes in existence today are descended from the Y chromosome of a single ancestor who LIVED about 100 years ago.