题目

 恒温恒压下，对于反应：A(g)＋3B(g)3C(g)，达到平衡状态的标志是     （    ）                                                                                            A． v正（A）= 3 v逆（C）               B．密闭容器内气体的密度不再改变 C．单位时间内消耗3n mol C的同时，生成3n mol B    D．密闭容器内气体的浓度之比为1:3:2The teachers’ office is on the ________ floor. ( )A. first B. one C. two