There are several reasons for this phenomenon. Here, it is best to quote some rules and figures. For example, the smog weather is caused by the fact that the exhaust emissions of nearby factories do not meet the national regulations. In a certain year, the state made clear regulations on the exhaust emission of factories, and the height of chimneys should not be less than several meters, and so on. For example, one right and one wrong, ancient and modern, Chinese and foreign, famous sayings and aphorisms and so on.
After explaining the reasons, we should solve them. Here, it is best to quote some examples. For example, a city has made a new plan for air pollution, and the air in the city is cleaner, and so on.
The end summarizes the full text and echoes the beginning.
This is a common total score format.