You ___________ wear a uniform! It's the rule. (should / must / may)
You must wear a uniform! It's the rule.
Children _____ (must / may / should) not eat too much chocolate. It's bad for their health.
Children should not eat too much chocolate. It's bad for their health.
Pam and Tim said they were very busy. Maybe they won't come. Pam and Tim________ (mustn't / shouldn't / may not) come.
Pam and Tim may not come.