stop doing/to do
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 restedB. restingC. 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。

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)

典型例题

---- The light in the office is still on.

---- Oh，I forgot___.

A. turning it offB. turn it offC. to turn it offD. 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。