He did not regret saying what he did but felt that he it differently.
A. could express
B. would express
C. could have expressed
D. must have expressed
网友回答
A. could express
B. would express
(答案→)C. could have expressed
D. must have expressed
解析：考查情态动词+have done的用法：could have done本可以做而没做，must have done过去一定做了，句意：他不后悔做得事情，只是感觉他可以做得更好（而实际没有）。选C。