一、祈使句自然可省去主语，如：
Leave him in peace! 不要去打扰他!
Come at one o'clock sharp. 准一点钟来。
Listen to me, children! 听我讲，孩子们!
Look both ways before you cross the road. 过马路之前要向两边看看。
二、除祈使句外，还有其他省去主语的情况，如：
Don't know. 我不知道。(省去主语I)
Beg your pardon. 请原谅。(省去主语I)
Had a good time, didn't you?玩得很好，不是吗?(省去主语you)
Doesn't look too well. 他脸色不大好。(省去主语he或she)
Looks like rain. 像是要下雨了。(省去主语it)
三、Must be somebody waiting for you. 一定是有人在等你。
Appears to be a big crowd in the hall. 大厅里似乎有一大群人。
