问题补充:
When he fell off the bike, he tried but couldn .
A. to have stood up
B. standing up
C. to stand up
D. having stood up
答案:
A. to have stood up
B. standing up
(答案→)C. to stand up
D. having stood up
解析:fall off the bike意为: 从自行车上跌下来,try to do sth.意为:尽力做某事。