You can’t imagine the difficulty he onto the cliff and saving the boy in trouble. A. had

问题补充：

You can’t imagine the difficulty he onto the cliff and saving the boy in trouble.

A. had to climb

B. had climbed

C. had climbing

D. had on climbing

答案：

A. had to climb

B. had climbed

(答案→)C. had climbing

D. had on climbing

解析：考查定语从句和非谓语动词。句意：你不能想象出他爬上悬崖就这个陷入困境的 男孩的困难。he had做后置定语修饰difficulty，现在分词作伴随状语表示正在进行的伴随性动作，和he是逻辑上的主谓关系。故选C。