To get to the top of the mountain we had to .A. go some walking 　B. do a lot of climbingC

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。