He failed in the exam and I wonder he studied hard in the school.A. whenB. thatC. ifD. w

问题补充：

He failed in the exam, and I wonder he studied hard in the school.

A. when

B. that

C. if

D. where

答案：

A. when

B. that

(答案→)C. if

D. where

解析：本题failed是关键词，C项符合题意，意为：是否。