GWD-17-38

lonelyplanet

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

key

but how can "have lived" comes with 140,000 years ago? I think the answer should be B.

chenjinchent

同意D.

to have done, 表完成.

lonelyplanet

如果是完成，140，000 years就可以了。加上ago，怎么表示从过去到现在呢？

AlphaBeta

ancestor’s后面应接whose.

kanstorys

不定式的完成时仅仅表示动作发生在前面那个动词之前，没有延续到现在的意思.