定语从句：关系代词作表语，用that不用which/who

My uncle is quite worn out from years of hard work. He is no longer the man ___ he was fifteen years ago. (2011英语专四51题)

A. Which    B. whom    C. who    D. that

答案：D

解析：关系代词在定语从句中做表语时，无论指人还是指物，通常用that，不用which或who，且that也可以省略。

再如：

1、China is not the country (that) it was. 中国不是从前的那个国家。

2、Mary is no longer the girl (that) she used to be. 玛丽不是过去的那个女孩了。