求助gwd17-38

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

A：省略chs，is错

B：was错，时态错

C：whom错，had错

E：whom错，had错

C合理，ancestor现在被认为曾经在140年前