c为什么要用musn't回答以 may 开头的疑问句有如下表达法：-May I smoke here? 我可以在这儿抽烟吗？-Yes, you may. / Yes, please. 请抽吧。-No, you can't. / No, you mustn't. / No, you'd better not. 请不要抽烟。