要看这个情态动词具体是什么含义,才能作答.
can 表能力的时候.Can you do it?---Yes,I can ./No,I can't.
can表可能的时候.Where can he be?----He may be in the office.用may回答.
can表许可的时候.can i smoke here?--no,you can't .yes ,you can.
may i ……?我可以……吗?表许可.yes,you may./no,you may not.
must i.和need i .回答一样.肯定回答是yes,you must.否定回答是no,you needn't/no ,you don;t have to.
有疑问欢迎追问!