Answer and explanation

Correct answer: A. mustn't

  1. Step 1: 'Mustn't' expresses prohibition.
Answer
mustn't.
Why not the others: "needn't" is wrong because 'needn't' means it is not necessary. "don't have to" is wrong because it means it is not necessary, which is not prohibition. "might not" is wrong because it expresses possibility rather than prohibition.

Practise more Passives, gerunds, infinitives and modals.

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