21. With a lot of difficult problems ______, the newly-elected president is having a hard time.

A. settled         B. settling         C. to settle               D. being settled

22. The man will have to wait all day ______ the doctor works faster.

A. if             B. unless           C. where                D. that

23. Who do you think the teacher will ______ the question?

A. have answer    B. have answered    C. have to answer      D. has answered