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

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 to do sth. 很遗憾地做...（事情还没有做）； regret doing sth. 后悔做了...（为已经做过的事而感到后悔），这里表示为已经做过的事而感到后悔，故选D