第二部分 英语知识运用（共两节，满分45分）
第一节 单项填空（共15小题；每小题1分，满分15分）
21. The chairman thought ______ necessary to invite Professor Smith to speak at the meeting.
A．that B. it C. this D. him
22. I failed in the last exam and only then __________ the importance of studies.
A. I realized B. I had realized C. had I realized D. did I realize
