must 开头的回答,肯定用Yes,you must.否定用No,you needn’t.
need 开头的回答,肯定用Yes,you need.否定用No,you needn’t.
should 开头的回答,肯定用Yes,you should.否定用No,you should not.
may 开头的回答,肯定用Yes,you　may.否定用No,you can’t.