问题补充：
He did not regret saying what he did but felt that heit differently.
A. could express
B. would express
C. could have expressed
D. must have expressed
答案：
A. could express
B. would express
(答案→)C. could have expressed
D. must have expressed
解析：考查情态动词。情态动词加动词原形表示对现在的推测。情态动词加完成时表示对过去的推测，有的情态动词像should have done, could have done, needn’t have done等有分别表示过去应该做某事却没有做；过去可以做某事却没有去做；过去不需要做某事却做了。（情态动词是否定形式的话，就是意思相反，shouldn’t have done表示过去不应该做某事却做了）
B可以表示过去将来时A选项的could 在这里表示能力但句子要表达的是“他觉得自己可以表达得不同的，但事实上没有”，所以选C，
