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