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（国家开放大学理工英语1）
Man-made air pollution mainly comes from two sources: mobile ones and stationary ones. Mobile sources are cars, planes, boats, etc. Stationary sources include large factories, power plants and every household, which burns natural gas or wood. The most important ways 回答
A
are to drive less, use less electricity and natural gas, and eat vegetarian.
A
are to drive less, use less electricity and natural gas, and eat vegetarian.
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