21．If you ____ your money ____ mine, we will have enough to buy one more set of stamps to ____ our collection.
A. join; in; add B. add; to; add to
C. put; to; add up D. add; in; add up to
22. ____finish their task ahead of time, the students worked harder and harder.
A. So as to B. As to C. In order to D. In order not to
23. You have no idea what I’ve had to ____ during the last few months.
A. come true B. go through C. come up D. look through
24. Taking plenty of exercise every day can make you full of ____, I think.
A. power B. strength C. energy D. force