This is just a short PowerPoint that might help to illustrate the difference between "don't have to" and "mustn't". At the end of the presentation I'll ask my students to come up with some sentences using "(don't) have to" and "must(n't)" and elaborate on them to help them understand the difference. For instance, if they say, "You musn't play tennis here. (It's dangerous!)" You should explain, "You must play tennis here. (and only here)", "You have to play tennis here.", and "You don't have to play tennis here. (you can play it other places too!)"
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