Choose the modal verbs which express: obligation and necessity: can must needn't may have to would offer: need shall could must would can lack of necessity: needn't don't have to can't mustn't don't need to couldn't prohibition: can't shouldn't mustn't don't have to wouldn't needn't ability: could should be able to have to may can deduction: must can't ought to might may could advice: shall must should have to ought to will