regret to do 對要做的事遺憾。 (未做)
regret doing 對做過的事遺憾、後悔。(已做)
i regret to have to do this, but i have no choice.
我很遺憾必須這樣去做，我實在沒有辦法。
i don't regret telling her what i thought.
我不為告訴她我的想法而後悔。
典型例題
---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. 對已發生的事感到遺憾。regret to do sth. 對將要做的事感到遺憾。本題為對已說的話感到後悔，因此選d。