21. The field research will take Joan and Paul about five months; it will be a long time _____ we meet them again.
A. after B. before C. since D. when
22. Little _______ that we were watching his every move, so he seemed to be going his own way in this business.
A. he realized B. he didn't realize C. didn't he realize D. did he realize
23. The teacher __ have thought Johnson was worth it or she wouldn't have wasted time on him, I suppose.
A. should B. can C. would D. must
24. -- Was Martin sorry for what he' d done?
-- ___________. It was just like him!
A. Never mind B. All right C. Not really D. Not surprisingly
