21. The problem he put forward at the meeting was _____. Which one of the following is WRONG?

A. worth thinking over                      B. worthy to consider          

C. worthy of being thought over             D. worthy of consideration

22. Tom, _____ yourself. Did you forget the school rules?

A. behave           B. believe                  C. perform          D. conduct

23. She has _____ the stars all her life, which she is proud of.

   A. noticed              B. observed             C. discovered       D. seen

24. Gun control is a subject _____ Americans have argued for a long time.

A. of which         B. with which           C. about which      D. into which