surprised me most was that he made the same mistake again.A. ItB. ThatC. WhatD. Which

问题补充：

surprised me most was that he made the same mistake again.

A. It

B. That

C. What

D. Which

答案：

A. It

B. That

(答案→)C. What

D. Which

解析： 考查主语从句。 surprised me most是主语从句，且从句缺少主语，所以选C。