问题补充:
To get to the top of the mountain, we had to .
A. go some walking
B. do a lot of climbing
C. walking a long way
D. doing a lot of climbing
答案:
A. go some walking
(答案→)B. do a lot of climbing
C. walking a long way
D. doing a lot of climbing
解析: have to后面跟动词原形。