题目

下列化学反应中，元素的化合价没有发生变化的是△   点燃    ①              ②      ③         ④    A.①②③                           B.①②④    C.②③④                           D.①③④ 答案：B There is very little ______ in protesting.It won’t help much. A.use                                                                                   B.meaning C.work                                                                                D.point