题目

It was        most of the students were unable to work out.A. too difficult a problem as      B. a too difficult problem that C. so difficult a problem that     D. such a difficult problem as 答案：D请根据要求写出文字表达式（第1～2小题请写出各物质对应的化学式）（1）镁带燃烧镁+氧气点燃氧化镁Mg O2 MgO镁+氧气点燃氧化镁Mg O2 MgO；（2）碳酸氢铵受热分解碳酸氢铵加热氨气+水+二氧化碳NH4HCO3 NH3 H2O CO2碳酸氢铵加热氨气+水+二氧化碳NH4HCO3 NH3 H2O CO2；（3）蜡烛在空气中燃烧石蜡+氧气点燃二氧化碳+水石蜡+氧气点燃二氧化碳+水．