Listen up, guys!Everyone ________ wear a mask. Go and buy one if you don’t have one.
句意：听着，大家！每个人都必须戴口罩。如果你没有，就去买一个。
考查情态动词。can’t不能；can可以；mustn’t禁止；must必须。根据“Everyone...wear amask. Go and buy one if you don’t have one.”可知，此处表示必须戴口罩，用must。故选D。
Listen up, guys!Everyone ________ wear a mask. Go and buy one if you don’t have one.
—Must I return this book before Friday, Sir?
—No, you ________,dear. You can keep it for two weeks.
You’d better take an umbrella when you go out, because it ________rain.
The man _______ be a doctor in this hospital, but I’m not sure.
—Whose notebook is this?
—It ________ be Alan’s. It looks like his.
Mary ________ go to London next year but she is not sure.
