(1) must出現在肯定陳述句中,表示"必須"的意思,此時疑問部分通常用"needn't"。
例句1:
You must take off your shoes when getting into the room, needn't you?
進入房間時你必須要脫掉鞋子,不是嗎
例句2:You must stay here and return the purse to the owner, needn't you?
你必須呆在這把錢包交還給失主,不是嗎
(2) must表示"必須"出現在否定陳述句中(即陳述部分用到must not或者mustn't,意思爲"不允許,禁止"),此時疑問部分通常用"must"或者用"may"。
例句1:You mustn't trample on the grass, must you/may you?你不能踐踏草坪,對吧
例句2:You mustn't smoke in public places, must you/may you?你不能在公共場合抽菸,對吧
(3) must出現在陳述部分作爲一種肯定的推測,表示"一定,肯定"的意思,此時疑問部分需要根據實際語意來確定。
例句1:He must be angry, isn't he?他肯定生氣了,對嗎
例句2:You must be hungry, aren't you?你肯定餓了,對吧
例句3:She must have got married, hasn't she?