【正确答案】正确答案： Air Pollution Air pollution consists of chemicals or particles in the air / that can harm the health of humans, animals, and plants. / Pollutants in the air take many forms. / They can be gases, solid particles, or liquid drops. / Pollution enters the Earth's atmosphere in many different ways. / Most air pollution is created by people, taking the form of emissions from factories, cars, or planes. / Second-hand cigarette smoke is also considered air pollution. / These are all man-made sources of pollution. / Some types of air pollution, such as smoke from wildfires or ash from volcanoes, occur naturally. / They are called natural sources. /