Do you want to teach the difference between must and have/has to in a context? Here's a helpful PDF worksheet which covers must and have to in the context of chores around the house. The worksheet is designed as A and B worksheets which will help increase classroom interaction.
Although must and have to can be a substitute for each other in many contexts, there is a very important difference between them, which is external and internal obligations. The worksheet is separated into two worksheets. Worksheet A covers external obligations and worksheet B covers internal obligations. During the activity students in two groups write different obligations for Susan and then swap their worksheets to check their partners. In this way, they'll have the chance to see modal verbs in proper contexts and have the opportunity to correct or discuss must or have to with their partners.