stop to do停止，中断做某事后去做另一件事。
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。
She reached the top of the hill and stopped ___on a big rock by the side of the path.
A. to have restedB. resting C. to restD. 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。
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.
Don't forget to come tomorrow.
---- The light in the office is still on.
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.
Don't you remember seeing the man before?
