As the world is getting more and more densely populated, air pollution has become a severe problem. Air pollution mainly derives from four major human activity sectors: industry, energy, transportation and agriculture. Energies are needed to run factories, to power trains, planes and buses. Nearly all of these energies are produced by burning fuels, which would cause air pollution. Scientists are studying new ways of generating electricity that can be less damaging to the environment. The increased public environmental awareness has led to the advent of activities such as recycling.
隨著世界人口越來越密集（densely populated），空氣污染已經(jīng)成了嚴(yán)重的問題?？諝馕廴局饕獊碓从谒膫€主要的人類活動領(lǐng)域：工業(yè)、能源業(yè)、交通運輸業(yè)以及農(nóng)業(yè)。經(jīng)營工廠，為火車、飛機(jī)和公共汽車提供動力都需要能源。幾乎所有這些能源都是通過燃燒燃料產(chǎn)生的，這就會造成空氣污染?？茖W(xué)家們正在研究能減少環(huán)境破壞的新發(fā)電方式。增強(qiáng)的公共環(huán)保意識使諸如回收利用（recycling）等活動產(chǎn)生。
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