从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21．There was time I hated to go to school .
A. a, that B. a, when C. the, that D. the, when
22. --Jenny took the 8:00 bus to Guangzhou this morning.
--Really? He __ ___the 9:00 train. It’s much more comfortable and safer to travel by train.
A. could have taken B. should take C. must have taken D. can take
23.The police suspected him of carrying drugs so they his bag, but found nothing.
A. looked up B. turned in C. searched for D. went through
24. -- The authors of computer viruses are geniuses.
-- I agree. They can apply their wisdom to other net technology __ ____ human beings can benefit.
