The gasoline burned in car engines is the main cause of air pollution in many cities. In order to reduce pollution, the number of cars on the roads must be reduced. This is only possible if fewer people drive their cars every day. Thus, if city governments want to improve the quality of the air in their city, they need to improve the
1.highway system.
2.quality of life in the city.
3.connections between cities.
4.public transportation system.