It might have been John bought a present for Mary yesterday.A. thatB. whenC. whatD. which

问题补充：

It might have been John bought a present for Mary yesterday.

A. that

B. when

C. what

D. which

答案：

(答案→)A. that

B. when

C. what

D. which

解析：考查强调句型，it is that……。本句中引导词指代前文内容，只是其中的动词be采用了might have been这一复杂结构。故引导词用that。选A。