This is certainly the case but it is a mistake or not I don’t know. A. ifB. even thoughC

问题补充：

This is certainly the case, but it is a mistake or not I don’t know.

A. if

B. even though

C. whether

D. that

答案：

A. if

B. even though

C. whether

D. that

解析：引导宾语从句时,whether 和if常可互换,但如从句提前,则只能用whether。