第二部分 英语知识运用(共两节，满分45分)
第一节 单项填空（共15小题；每小题1分，满分15分）
21. Although everything seems to have been taken into consideration，______ accident can happen when the astronauts walk in _______ space.
A. /; the B. an; the C. the; the D. an; /
22. ［2012安徽皖南八校］Shenzhou Ⅷ has docked with Tiangong-1 successfully, ______ the start of the establishment of China’s own space station.
A. marked B. to mark
C. marking D. having marked
23. Five of the twelve bronze animal heads _______ to China, with seven other ones still missing.
A. returned B. had returned
C. have been returned D. have returned
