can't ; needn't; mustn't; must
—Yes. The food there be delicious.
—No, you . You can clean it after school.
(必须) match?
—No, you (mustn't/can't/needn't). You (can/must) do your homework first.
—Okay, Jim, call me when you get there.
From now on, we must rubbish into the river.