A、Industries and government eontribute another 20 percent: the largest industrial polluters are petroleum refineries.
B、The air we breathe is about one-fifth oxygen and a little less than four-fifths nitrogen (氮), with traces of other gases,water vapor, and the waste products we put into it.
C、Homes, apartments, and offices use coal, gas and oil for heat.
D、Motor vehicles account for over 51 percent of the total polluting material sent into the atmosphere every year.
E、Heating is also a major source of pollution.
F、Most air pollution is caused by the gasoline-powered internal combustion(燃烧)engines of cars , trucks and buses.
G、Another source of pollution is the incineration (烧成灰烬)of garbage, trash,metal,glass, and other waste.
H、Electrical power plants also contribute about 20 percent of the total air pollutants by burning coal or oil for electrical power.
