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

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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。