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Cars, being the greatest source of air pollution, can be left at home this weekend.
汽车是空气的主要污染源，这个周末可以别开车了。
youdao
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It is a main source of air pollution in cities.
它是城市主要的空气污染源。
youdao
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It is a main source of air pollution in cities.
它是城市主要的空气污染源。
youdao