regret to do   对要做的事遗憾。          (未做)
    regret doing   对做过的事遗憾、后悔。    (已做)
    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 don't 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。