7.--- May I go swimming now?

7.--- May I go swimming now?
--- No,you ______.You must finish your homework first.
A.mustn’t B.may not C.couldn’t D.needn’t [1298]
8.--- Excuse me.Where is the zoo?
--- Sorry,I don’t know.Ask that policeman.He _____ know.
A.shall B.may C.need D.would [1299]
但是mustn't不是禁的意思吗？