You mustn't forget your appointent at 3 o'clock.
You must remember that we've got an apointment at 3 oc'clock
It must be raining.
It mustn't smoke at school
You must stop drinking.
You mustnt drinking this water.
You must be hungry
You mustn't go against go against your parents' wishes.
You must play the piano on a daily basis
Your mustn't play the piano beyond 8 p.m.