-----You were brave enough to raise objections at the meeting.　　-----Well now I regret th

问题补充：

-----You were brave enough to raise objections at the meeting.

-----Well, now I regret that.

A. to do

B. to be doing

C. to have done

D. having done

答案：

A. to do

B. to be doing

C. to have done

(答案→)D. having done

解析： regret doing sth.后悔作了什么。