impressed me most about the woman was that she looked after the old man for twenty years

问题补充：

impressed me most about the woman was that she looked after the old man for twenty years without any complaint.

A. That

B. Which

C. What

D. As

答案：

A. That

B. Which

(答案→)C. What

D. As

解析：词义辨析。A. 那个 B.哪一个 C. 什么 D. 由于；句意：关于这个女人给我们印象最深的是她毫无怨言的照顾了这位老人二十年。主语从句缺少主语，故选C。