The air pollution in underground garages has become more and more serious in recent years.
近年来，地下车库空气污染越来越严重。
Air pollution on underground trains tend to be less toxic than that at street level.
地铁里的空气污染应该比街道的毒性弱。
Air pollution on underground trains tend to be less toxic than that at street level.
地铁里的空气污染应该比街道的毒性弱。
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