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
