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. The sentences cover a variety of situations involving obligations, prohibitions, recommendations, and permissions regarding work, health, school rules, and social etiquette. Completing the sentences correctly requires understanding the meanings and uses of these modal verbs.