forget doing/to do
forget to do 忘记要去做某事。 (未做)
forget doing 忘记做过某事。 (已做)
The light in the office is stil on. He forgot to turn it off. 办公室的灯还在亮着，它忘记关了。(没有做关灯的动作)
He forgot turning the light off. 他忘记他已经关了灯了。( 已做过关灯的动作)
Don't forget to come tomorrow. 别忘了明天来。(to come动作未做)
---- The light in the office is still on.
---- Oh, I forgot___.
A. turning it off B. turn it off C. to turn it off D. having turned it off
答案：C。由the light is still on 可知灯亮着，即关灯的动作没有发生，因此用forget to do sth.
而forget doing sth表示灯已经关上了，而自己忘记了这一事实。此处不符合题意。
remember doing/to do
remember to do 记得去做某事 (未做)
remember doing 记得做过某事 (已做)
Remember to go to the post office after school. 记着放学后去趟邮局。
Don't you remember seeing the man before? 你不记得以前见过那个人吗?
regret doing/to do
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。
---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。
cease doing/to do
cease to do 长时间，甚至永远停做某事。
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