The relationship between air and human body. This composition is 400 words.

These days, the fog has filled the whole campus, and it seems that rain can be smelled in the humid air. Especially when you travel in the morning, half of the roads are foggy, and you can't see people or the surrounding greenery. During the day, the lights are also on. In order to prevent the fog from spreading, all the campuses in the city have entered the smog area these days.

Although people have made great efforts to protect the environment, it can't be completed overnight. In the past, a large number of trees were cut down and roads and bridges were built, which increased the silt in the river bed. Once it rains, the riverbank will be out of control, and the river will overflow into the fields, causing no small flood disaster. Moreover, under the influence of chemical enterprises, the air quality is greatly reduced, more and more houses are built, greening is gradually replaced by high-rise buildings, chimneys, waste gas and garbage follow one after another, so there is smog.