题目

 — I saw Tom in the school just now.    — No, it ________ him. He left for London last week.  A. can be             B. must be          C. mustn’t be        D. can’t be 答案：D下列变化不能通过一步化学反应实现的是（ ）A. BaCl2→BaSO4B. CuO→Cu(OH)2C. NaOH→Na2SO3D. MgSO4→Mg(OH)2