He did not regret saying what he did but felt that he it differently.A. could expressB.

问题补充：

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

答案：

A. could express

B. would express

(答案→)C. could have expressed

D. must have expressed

解析：掌握情态动词的完成结构的用法是解此题的关键，could express过去能够表达；would express(过去)将要表达；could have expressed本来能够表达；must have expressed(表推测)肯定能表达。