As the proverb goes, beggars______ be choosers．

A．can’t          B．mustn’t        C．shouldn’t         D．needn’t

I don't believe him; he ________ be serious.

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I don't believe him; he ________ be serious.

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There’s no light on ― they          be at home.

       A．can’t                   B．mustn’t               C．needn’t               D．shouldn’t

Tina _____ have known the truth, or she would have told us.