(must/can/may)i return the magazine tomorrow?yes.you(must/ca

(must/can/may)i return the magazine tomorrow?yes.you(must/can/may).
must是只能用在肯定句中吗?

May i return the magazine tomorrow?yes.you can.
一、 can,could
1) 表示能力（体力、知识、技能）.
Can you lift this heavy box?（体力）
Mary can speak three languages.（知识）
Can you skate?（技能）
此时可用be able to代替.Can只有一般现在时和一般过去式；而be able to则有更多的时态.
I’ll not be able to come this afternoon.
当表示“经过努力才得以做成功某事”时应用be able to,不能用Can.如：
He was able to go to the party yesterday evening in spite of the heavy rain.
2) 表示请求和允许.
-----Can I go now?
----- Yes,you can./ No,you can’t.
此时可与may互换.在疑问句中还可用could,
might代替,不是过去式,只是语气更委婉,不能用于肯定句和答语中.
---- Could I come to see you tomorrow?
---- Yes,you can.( No,I’m afraid not.)
3) 表示客观可能性（客观原因形成的能力）.
They’ve changed the timetable,so we can go by bus instead.
This hall can hold 500 people at least.
4) 表示推测（惊讶、怀疑、不相信的态度）,用于疑问句、否定句和感叹句中.
Can this be true?
This can’t be done by him.
How can this be true?
二、 may,might
1) 表示请求和允许.might比 may语气更委婉,而不是过去式.否定回答时可用can’t
或mustn’t,表示“不可以,禁止”.
----Might/ May I smoke in this room?
---- No,you mustn’t.
---- May/Might I take this book out of the room?
---- Yes,you can.(No,you can’t / mustn’t.)
用May I...征徇对方许可时比较正式和客气,而用Can I...在口语中更常见.
2）用于祈使句,表示祝愿.
May you succeed!
3) 表示推测、可能性（不用于疑问句）.
might不是过去式,它所表示的可能性比may小.
1．He may /might be very busy now.
2．Your mother may /might not know the truth.
三、 must,have to
1) 表示必须、必要.
You must come in time.
在回答引出的问句时,如果是否定的,不能用mustn’t（禁止,不准）,而用needn’t,don’t have to（不必）.
---- Must we hand in our exercise books today?
---- Yes,you must.
---- No,you don’t have to / you needn’t.
2) must是说话人的主观看法,而have to则强调客观需要.Must只有一般现在时,have to 有更多的时态形式.
1． he play isn’t interesting,I really must go now.
2． I had to work when I was your age.
3) 表示推测、可能性（只用于肯定的陈述句）
1． You’re Tom’s good friend,so you must know what he likes best.
2． Your mother must be waiting for you now.