The air we breathe is so freely available that we take it for granted. Yet without it we could not survive more than a few minutes. For the most part, the same air is available to everyone, and everyone needs it. Some people use the air to

北京等多地PM2.5浓度爆表，空气质量指数将达到极重污染。国内的多家英语报纸网站都刊载了大量有关雾霾锁城的报道。我们先来看看