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

网友回答

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。