Many cities have problems with air pollution and smog. What can big cities do to regulate the amount of air pollution and smog generated by cars and factories?

许多城市面临着空气污染和烟雾的问题，这些大城市能够在控制空气污染，汽车和工厂产生的烟雾的问题上做些什么呢？

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As many cities are constantly expanding around the world, the environmental effect and the revegetation of landfill have become very urgent and outstanding problems.

随着世界各地城市市区的不断扩大，垃圾填埋场的环境影响和植被重建已成为全球所共同面临的一个相当紧迫和突出的环境问题。

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But during the course of the restructuring of many cities in the world, some problems have been caused, such as more layoffs, the descend in public finance income and the residents' life level.

但从目前来看世界上的矿业城市在转型过程中多数曾引发了诸如下岗人员增多，财政收入锐减、居民生活水平相对下降等问题。

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Many other cities have problems like Delhi's, though mostly in less extreme forms.

ECONOMIST: It must also be clean