mustn't (不可以；禁止)
May I go now? No, you mustn't. 我可以走了吗？不可以。
You must keep it a secret. You mustn't tell it to any one.
你一定要保守秘密，不可以告诉任何人。
You mustn't make noise. We are having a meeting.
你不可以吵闹，我们正在开会。
You mustn't turn the switch on; the room is full of gas.
你不可以将开关打开，房间里充满了瓦斯。
Children mustn't play with dangerous objects like sharp knives or scissors.
小孩子不可以玩危险的物品，例如锐利的刀子或剪刀。
This is an opportunity that comes once in a lifetime. You mustn't let it pass.
这是一生难逢的机会，你绝不可放过。
