Module 12 Help模块自测 一、单项填空(10分) (C)1.-What's behind ________ door? I can't open it. -Let me see. Oh, there is a ball. A. a B. an C. the D. / (A)2.-Must we clean the classroom right now? -No, you needn't, but you ________ do it today. A. must B. mustn't C. may D. needn't (D)3.-Whose is the notebook? -I'm not sure. It ________ be Mary's. A. must B. mustn't C. needn't D. could (C)4.He lives on the 30th floor an..