GWD 17-38

qiancheng

 

Q38:All Y chromosomes in existence today are descended from a single ancestor’s who is thought to have lived about 140,000 years ago.

1. a single ancestor’s who is thought to have lived
2. a single ancestor’s who was thought to live
3. a single ancestor whom it is thought had lived
4. the Y chromosome of a single ancestor who is thought to have lived
5. the Y chromosome of a single ancestor whom it was thought had lived

请问D的时态该怎么解释啊，前面讨论的贴子也没解释清楚

casualwalk

who　is thought说明了是现在最认为。。

Jarod

 a single ancestor who is thought to have lived about 140,000 years ago.

强调一种时间上的比较， is thought泛指现在或者公认， 而to have lived 呼应后面的时间状语about 140,000 years ago， 和is thought形成时间对比。

celinapple

是不是主要表达曾经的意思