—____________ we leave the library before 5 o'clock?
—No, you needn't. You can stay here until 5:30.
句意：——我们必须在五点钟之前离开图书馆么？——不，你没必要。你可以在这儿待到五点半。
考查情态动词。must必须；may可能；can能够，可以。根据“No, you needn't. Youcan stay here until 5:30”可知问句表达的是“是不是必须在五点钟之前离开图书馆”，用情态动词must提问，否定回答用needn't表示没有必要。故选A。
—____________ we leave the library before 5 o'clock?
—No, you needn't. You can stay here until 5:30.
The biggest challenge weall face is to prevent further environmental disasters. We ________ take action before it is too late.
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.
