4. 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 ?

5. 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。
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 。

6. cease doing/to do

cease to do 长时间，甚至永远停做某事。
cease doing 短时停止做某事，以后还会接着做。
That department has ceased to exist forever.
那个部门已不复存在。
The girls ceased chatting for a moment when their teacher passed by.