The chairman thought necessary to invite Professor Smith to speak at the meeting.A. thatB

问题补充：

The chairman thought necessary to invite Professor Smith to speak at the meeting.

A. that

B. it

C. this

D. him

答案：

A. that

(答案→)B. it

C. this

D. him

解析：

这是考查it做形式宾语的用法，think it+adj/n+to do sth…,这里的不定式是真正的主语。句意是：主席认为邀请Smith在会议上演讲是必要的。