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