题目

下列反应属于氧化还原反应的是(   )   A.CaO＋H2O==Ca(OH)2                       B.Fe2O3＋3CO2Fe＋3CO2   C.CaCO3CaO＋CO2↑                   D.CO2＋2NaOH==Na2CO3＋H2O 答案：B--- Shall we go out for a walk around Prague? --- I’m afraid not. We can’t go out         our work is being done. A．before            B．until            C．as          D．after