Today, no huge improvement for the automobile or airplane is in sight, and the major struggle is to limit their pollution, not to vastly improve their capabilities.

今天，在汽车或者飞机上没有值得一提的较大的改进，但这些都是在限制污染上大费周章，而并不是在性能上的大幅改善。

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In order to create an environmentally friendly and safe world, it is necessary for each country to set vehicular quotas and limit the permits in number to control regional air pollution.

为了创造一个有益于环保和安全的世界，每个国家都有必要定出汽车限额，并限制发放许可证的数量，以控制地区的空气污染。

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Two approaches are on offer. Some think the best way to limit emissions is to tax them; others argue for a system that sets a cap on pollution, and lets polluters trade the right to emit.

可供选择的方法有两种：有的人认为向排放物征税是最佳的限制手段；其他人支持一种对污染物施加管制的方案，并允许污染者将排放权进行交易。

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Stephen Hardwick, from the British Airport Authority, which runs Heathrow, Gatwick and Stanstead said efforts were already being made to limit the impact of noise and air pollution and road congestion around the airports.

BBC: Delays at a London airport

At issue now is the Cross-State Air Pollution Rule that attempts to limit the levels of harmful emissions as they traverse across state lines.

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There's no example of an air pollution problem anywhere in the world that has been solved without a cap or legal limit on how much of that pollution can be dumped into the sky.

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