— Dad, must I practice the violin today?— No, you __________. You __________ do it tomorrow.A., mustn’t, may B. needn’t, may C. shouldn’t, can D. needn’t, mustn’t 答案:B下列各物质均含有N元素,在这些物质中N元素的化合价最低的一种是A.KNO3???????? B.NH4Cl????????? C.NO????????????? D.NO2