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。