Question

need't be,can't be,may not be和mustn't有什么区别

Answer 1

needn't be没必
can't be不能
may not be也许不
mustn't禁止
can't be和mustn't都指不能做某事，但后者语气较强，表示绝对不能。

Answer 2

一般来讲.must带有强制愿望.相较而言感情色情更强烈些.
而need.may.can.感情色彩偏向中等.一般愿望.可有主观意愿.must主在强制意味.不得不.必须.

Answer 3

needn't be不需要 can't be不能 may not be也许不 mustn't禁止