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

问题补充：

—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

答案：

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。