21._____ of the students who took part in the military training is 450.
A. A number B. A lot C. Lots D. The number
22.Rather than ______ on a crowded bus, he always prefers _______a bicycle．
A.ride; ride B.riding; ride C.ride; to ride D.to ride; riding
23._____ he is determined to do something, no one is able to make him ______.
A. Once; give up B. Although; give in
C. As long as; give out D. If; give away
