2个回答
mustn't 语气强，”禁止”;千万不要的意思 例如:You mustn't step on the grass.
needn't 表示不必这么做：常做must问句的回答：Must I finish my homework today? No, you needn't.
can't ”不能”; You can't be too serious;问句回答时：Can I go out to play? No, you can't. 或做may问句的回答：May I sit here? No, you can't.;
shoudn't语气较委婉，”不应该”
maynot语气较弱，”可以不”，youmaynotfinishyourhomework;
can't”不能”;youcan'tbetooserious;问句回答时：canigoouttoplay?no,youcan't.或做may问句的回答：mayisithere?no,youcan't.;
couldn't语气较委婉，”不能”,常做could疑问句的回答：couldisithere?i'mafraideyoucouldn't;
needn't表示不必这么做：常做must问句的回答：mustifinishmyhomeworktoday?no,youneedn't.
mustn't语气强，”禁止”:youmustn'tsteponthegrass.