气体
1.We have reduced emission of air pollutants in recent years, but cars are still a major source of them. Factories have become cleaner as stricter environment pollution law have been introduced.
我们这些年也在减少有害气体排放量，但是汽车废气排放依然是空气污染的主要原因.随着环境保护法的颁布。工业废气排放没有以前严重了。
