题目

Where do most of the woman's earnings come from now? A . Her recordings. B . Her advertising work. C . Her concert performance. 答案：B一种焰火火药中所含的硝酸铜在燃烧时放出绿色火焰，发生如下反应：2Cu（NO3）2   △  . 2CuO+O2↑+4X↑    其中X是一种污染空气的有毒气体，根据质量守恒定律，推测X是（　　）A．NOB．NO2C．N2OD．N2O5