When was it you met him in the library?A. as B. thatC. whileD. if.

问题补充：

When was it you met him in the library?

A. as

B. that

C. while

D. if.

答案：

A. as

(答案→)B. that

C. while

D. if.

解析：考查强调句型。本题是强调句型的特殊疑问句，强调的是时间状语，本题是对时间状语的提问。句意：究竟是在什么时候你在图书馆里遇见他的？故B正确。