第二部分 英语知识运用(共两节，满分35分)
第一节 语法和词汇知识（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合肥模拟］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
