—You were brave enough to raise objection at the meeting.
—Well, now I regret that.
A. to do
B. to be doing
C. to have done
D. having done
网友回答
A. to do
B. to be doing
C. to have done
(答案→)D. having done
解析：regret doing sth 表示对已经发生的事感到“后悔”；regret to say / tell / inform / announce 用以报告令人不快之事，表示对将要说的话感到“遗憾、抱歉”，主语通常是 I / we, regret 用一般现在时。