题目

能正确表示下列化学反应的离子方程式的是                         A．氢氧化铜溶液与盐酸的反应     OH-＋H+ ＝ H2O B．澄清的石灰水与稀盐酸反应  Ca(OH)2 + 2H+ = Ca2+ + 2H2O C．铜片插入硝酸银溶液中  Cu + Ag+ = Cu2+ + Ag D．碳酸钙溶于稀盐酸中   CaCO3＋2H+＝Ca2+＋H2O＋CO2?? 答案：D 解析: 略15、 In our class, when the bell rang and the teacher closed his book, it was a ______ for everyone to stand up. A. signal        B. chance          C. mark            D. measure