A report published recently brings bad news about air pollution. It suggests that it could be as damaging to our health as expos

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问题     A report published recently brings bad news about air pollution. It suggests that it could be as damaging to our health as exposure to the radiation from the 1986 Ukraine nuclear power disaster. The report was published by the UK Royal Commission on Environmental Pollution.  But what can city people do to reduce exposure to air pollution? Quite a lot, it turns out.
    Avoid walking in busy streets. Choose side streets and parks instead. Pollution levels can fall a considerable amount just by moving a few meters away from the main pollution source—exhaust fumes (烟气). Also don’t walk behind smokers. Walk on the windward side of the street where exposure to pollutants can be 50 percent less than on the downwind side.
    Sitting on the driver’s side of a bus can increase your exposure by 10 percent, compared with sitting on the side nearest the pavement. Sitting upstairs on a double-decker can reduce exposure. It is difficult to say whether traveling on an underground train is better or worse than taking the bus. Air pollution on underground trains tends to be less toxic than that at street level, because underground pollution is mostly made up of tiny iron particles thrown up by wheels hitting the rails. But diesel and petrol fumes have a mixture of pollutants.
    When you are crossing a road, stand well back from the curb while you wait for the light to change. Every meter really does count when you are close to traffic.  As the traffic begins to move, fumes can be reduced in just a few seconds.  So holding your breath for just a moment can make a difference, even though it might sound silly.
    There are large sudden pollution increases during rush hours.  Pollution levels fall during nighttime. The time of year also makes a big difference.  Pollution levels tend to be at their lowest during spring and autumn when winds are freshest. Extreme cold or hot weather has a trapping effect and tends to cause a build-up of pollutants.  
What is the passage mainly about?

选项 A、How to fight air pollution in big cities.
B、How to avoid air pollution in big cities.
C、How to breathe fresh air in big cities.
D、How serious air pollution is in big cities.

答案B

解析 第一段第四句是全文的主题句:城市居民如何减少接触被污染的空气。
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