In fact I wonder my efforts were all in vain.A. thatB. whichC. whyD. where

问题补充：

In fact, I wonder my efforts were all in vain.

A. that

B. which

C. why

D. where

答案：

A. that

B. which

(答案→)C. why

D. where

解析：考查宾语从句的连接词：句意：事实上，我想知道我的努力为什么会是徒劳。因为主句的谓语是wonder，应该用疑问词连接，which可以做主宾表，这句话不缺主宾表，where在哪里，不符合句意，选C。