1)The girl is rather young; she mustn't/can't be awake so late.
2)I think you mustn't/can't work harder.
3)Mustn't/can't you sit still?
4)The car is his father's we mustn't/can't take it.
5)Our teacher mustn't/can't be late for the classes either.
6)The water is rather hot, but l think you mast/candrink it.
7)The soldiers musr/can obey their officers.
8)You must/can pay for your lunch yourself if you want.
9)Must/can l use your bathroom?
10)l must/can work harder, so l may be helpful.