The theory he had stuck to be true.A. provedB. to provingC. to proveD. to proved

问题补充：

The theory he had stuck to be true.

A. proved

B. to proving

C. to prove

D. to proved

答案：

@@A. proved@@B. to proving@@C. to prove@@(答案→)D. to proved

解析：一看这四个选项认为是不定式后接动词原形，其实he had stuck to是充当后置定语，stick to(坚持)为一个固定搭配，去掉这个定语从句后，我们可以很清楚地发现整个句子缺少了谓语动词，定语从句时态为过去完成时，所以主句谓语动词应该过去式。