题目

Smoggy weather struck the north of China over and over again, it had a great effect on our life and health. Air pollution actual jumped to alarming levels last month, according to the  weather report. As a result, we always became concerned about PM2.5, high level of which does great damages to us. As we know, it is heavy traffic jams and the development of industry that has caused heavy pollution. Exposed to such a bad weather, what should we do protect our environment?                                     First, we can hold a speech contest abo氧气变成液氧是由于A.分子组成发生了变化B.分子间的间隙发生了变化C.分子的性质发生了变化D.分子运动停止了