She should buy a new house. She needs something bigger. / She ________ to buy a new house. She needs something bigger.
ought
Is it necessary to use that teapot? Can't you just put a teabag in a mug? / Do you _______ to use that teapot? Can't you just put a teabag in a mug?
have / need
It's really dangerous to drive when you're taking these tablets. / You _________ drive when you're taking these tablets. It's really dangerous.
mustn't