all cities.)\rMore and more factories are being set up every year and theses factories pour\rmillions upon millions of tons of harmful gases into the air. Power plants that\rburn coal add greatly to air pollution. Cars, which are out on the street, take in\rair and replace it with poisonous gases.\r(Now, more and more people are realizing the importance of clean air and\rtrying hard to prevent and control air pollution.) Schools are now teaching\rabout the pollution problem. Much money has been spent in cleaning up the air.\rIndustries are beginning to help clean up. They are installing special equipment\rto clean up their smoke. Scientists and engineers are trying to develop cleaner\rengines for cars. The day will come when people will be able to take in clean\rair in cities.
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