stop to do 停止，中断做某事后去做另一件事。
stop doing 停止做某事。
They stop to smoke a cigarette. 他们停下来，抽了根烟。
I must stop smoking. 我必须戒烟了。
典型例题
She reached the top of the hill and stopped ___ on a big rock by the side of the path.
A. to have rested B. resting C. to rest D. rest
答案：C。由题意可知，她到了山顶，停下来在一个路边的大石头上休息。因此，应选择stop to do sth. 停下来去做另一件事。而不仅仅是爬山动作的终止，所以stop doing sth.不正确。
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)
Dont forget to come tomorrow.
别忘了明天来。 (to come动作未做)
典型例题
---- 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 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。
Dont you remember seeing the man before?
你不记得以前见过那个人吗?