This document contains a grammar exercise where students must complete sentences with the modal verbs MUST, MUSTN'T, SHOULD, SHOULDN'T, HAVE TO, or DON'T HAVE TO/DOESN'T HAVE TO to demonstrate understanding of obligation and permission. The sentences cover a range of topics including work, health, school rules, and social etiquette. Completing the exercise requires analyzing the context of each sentence to determine whether the action is obligatory, prohibited, recommended, or optional.