The rule as a picture, 5 multiple-choice questions, 3 sentences to correct and a short writing task. Free to print and copy for your class or for self-study.
Want the explanation first? Read the Mustn't vs Don't Have To lesson
Mustn't means it's not allowed: You mustn't smoke here. Don't have to means it's not necessary, but you can if you want: You don't have to come. They look similar but mean very different things.
You mustn't talk during the exam.
You don't have to answer every question.
Write two sentences about your own life: one with Mustn't and one with Don't have to. Then explain the difference to a partner.
Answers will vary. Check that each sentence follows the rule on page 1, or paste them into Clarigram to have them checked.