Mum,may i go out to play ? -No,you ( ) .you must finish your homework first如何回答

问题描述:

Mum,may i go out to play ? -No,you ( ) .you must finish your homework first如何回答
A.may not B.mustn't C.couldn't D.needn't
参考答案选B,我觉得有问题

No, you mustn't 选 B . may的否定回答用mustn't 和can't. 这里couldn't是过去时