To his disappointment, the opinion he had stuck out wrong.
A. to turn
B. to turning
C. to turned
D. to be turned
网友回答
A. to turn
B. to turning
(答案→)C. to turned
D. to be turned
解析：句中He had stuck to是定语从句，修饰the opinion的，句中缺少谓语动词根据句意，用一般过去时态。句意：令他失望的是，他坚持的意见被证明是错的。