什么时候回答用needn't啊?象回答must的否定要用needn't.有没有一些情态动词的肯定和否定回答啊?还有语气关系是怎么样啊?

看意思,如果是不必,那就用needn't.
回答must的句子,如果是否定,就用needn't
比如
Must I come tomorrow?
No,you needn't.
另外的情态动词的例子.如果别人提供帮助,那要客气回答,有以下两种.
May I help you.
Yes,please./ No,thanks.
Can I help you.(帮忙)回答同上.
Can I ask for a day off.( 请假)
Yes,you can.(准假)/ No,you can't.(不准)