regret to do 对将要做的事遗憾，regret doing 对做过的事遗憾、后悔。例如：
I regret to have to do this， but I have no choice. 我很遗憾必须这样去做，我实在没有办法。
I dont regret telling her what I thought. 我不为告诉她我的想法而后悔。
典型例题
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：D.regret having done sth. 对已发生的事感到遗憾。regret to do sth. 对将要做的事感到遗憾。本题为对已说的话感到后悔，因此选D.