may i use your pen
Yes,you can
no,you may not.or you mustn't
Need i start from the beginning
yes,you must
no,you needn't.
注意：needn't have done“表示本来不必做某事而实际上做了某事”.例如：You needn't have waited for me.
Must we hand in our exercise books today?
Yes,you must.
No,you don’t have to.
Could I come to see you tomorrow?
Yes,you can.
No,I'm afraid not.