从A.B.C.D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. Going on a trip into ______ space must be quite ______ exciting experience.
A. / ; the B. / ; an C. the; an D. the; a
22. ______ many times, he finally understood it.
A. Told B. Telling C. Having told D. Having been told
23. Chen Xiexia is the first Chinese athlete ______ the gold medal in the Beijing Olympic Games.
A. winning B. to win C. wins D. won
24. At this time tomorrow ______ over the Atlantic.
A. we’re going to fly B. we’ll fly
C. we’ll be flying D. we’re to fly
25. Great attention must be paid ______ welfare, especially in the poor area.
A. develop B. to develop C. to developing D. developing
