一道语法题，来讨论下

38. GWD17-Q38:
        有ago可以用完成时吗
            

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

A.      a single ancestor’s who is thought to have lived

B.       a single ancestor’s who was thought to live

C.      a single ancestor whom it is thought had lived

D.      the Y chromosome of a single ancestor who is thought to have lived

E.       the Y chromosome of a single ancestor whom it was thought had lived

正确答案d ，我选了b ，why？

B选项没有D选项好有两个原因：
1. a single ancestor's Y chromosomes who was...中关系带词who与其要修饰的ancestor中其实还隔了一个被省略的Y。（尽量靠近修饰对像）
2. who was thought to live 这里没有用一般现在时好，因为它表达的是一个客观的科学观念。

然后，have lived 140,000 years ago在这里翻译出来就比较好理解了：一个在140，000年以前就已经活（在这个世上了） 不过，这里我也觉得用have lived since 140,000 years ago会比较好（虽然这个知识点没有干扰选项）但是我想题目这样用定有其深意，还请NN指点。