七
        Air Pollution
        根据所给的题目和下面的关键词，写一篇120个词左右的短文：
        
        health , surrounded by , smog , anything but , gases , impurities , absorb , poisonous , try hard , blacked out
        
        We all know that clean air is important to good health. Wherever you go and whatever you do, you are always surrounded by a sea of gases that we call air. If there are impurities in the air, they may be absorbed by our bodies and make us ill. We need clean air, but unfortunately , air pollution is globally present , especially in cities.
        
        Many large cities are anything but pollution-free. Our cities have many factories, which we need to make food, clothing and other things. Every year these factories pour millions upon millions of tons of smog into air. Power plants and houses that burn coal add greatly to air pollution. Besides , there are more cars in cities now. Once out on the streets, they will take in fresh air and replace it with poisonous gases.
        Our country is trying hard to prevent and control air pollution. As long as every citizen also realizes its importance and makes join efforts, the day will come soon when people will take in only clean air. Then , the sunlight will no longer be blackened out by smoke and soot.