上节课讲的是“不必（做某事）”，用 don't/doesn't have to，needn't (need not)，don't/doesn't need to，这节课我们讲 

mustn't (must not)
不能……

You mustn't play here – it's dangerous!
你不能在这里玩，这很危险！

He mustn't eat peanuts. He's allergic to nuts.
他不能吃花生。他对坚果过敏。
peanut(s) 花生（pea 豌豆 + nut坚果）
allergic 过敏的
be allergic to 对……过敏

You must not park outside the entrance.
你不能把车停在入口外。
park 动词，停（车）
entrance 入口

You must not make noise after 9 o'clock.
9点钟以后你不能吵闹。

不允许做某事也可以用 can't：
You can't go out tonight. You've got homework.
你今晚不能出去，你有作业要做。