题目信息
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
参考答案及共享解析
共享解析来源为网络权威资源、GMAT高分考生等； 如有疑问，欢迎在评论区提问与讨论
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已选答案：
正确答案：
D:the Y chromosome of a single ancestor who is thought to have lived
考点 用语 代词
Y chromosomes are descended from后面是接Y chromosomes或a single ancestor's（省略Y chromosome），
由此排除C。
who不可指代ancestor's排除AB。
a single ancestor 在thought to have lived/it was thought had lived中做have lived/had lived的主语，所以代词应该用who而不是whom，排除E。
故，答案为D。
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题目来源
GWD
