Modal verbs
3. She must wear a uniform. --> (por ley)
4. We don't have to go to school at weekends --> (falta de obligación)
7. It must be Tina. She promised to phone me. --> (promesa)
8. You shouldn't eat so much fast food. It's bad for your health. --> (consejo)
Must: strong obligation
don't have to: lack of obligation
shouldn't: advice
