就是通过打扫卫生，使污浊的环境重新变得自然干净。
By cleaning up-by getting back to natural wholesome conditions.
北京——每天大约有1000辆新车上路，使本来已经污浊不堪的城市更加拥挤。
BEIJING — Nearly 1,000 new cars hit the streets here every day, crowding a city already choked with pollution.
如果育雏室内通风不良，氧气就会逐渐减少，二氧化碳浓度增大，使空气变得污浊起来。
If the brood indoor and ventilated bad, oxygen will gradually reduce the concentration of carbon dioxide, air pollution, increase become up.
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