Wind is a clean source of renewable energy that produces no air or water pollution.
风是一种清洁的可再生能源，不产生空气和水污染。
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。
Uncontrolled it is a serious source of air pollution.
如果不进行控制将造成很严重的环境污染。
It is a main source of air pollution in cities.
它是城市主要的空气污染源。
It is a main source of air pollution in cities.
它是城市主要的空气污染源。
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