I regret that I am unable to help you.A. sayingB. sayC. to sayD. said

问题补充：

I regret that I am unable to help you.

A. saying

B. say

C. to say

D. said

答案：

A. saying

B. say

(答案→)C. to say

D. said

解析：习语搭配。regret to do sth “遗憾地去做某事” 很遗憾的告诉你我不能帮你。 选C