Direction：It is now generally accepted that vehicles (cars, trucks, etc.) are a major source of air pollution in cities. Your are to suggest only ONE way to solve the problem：One way to solve the problem

范文：
We all know that vehicles are the major source of air pollution in cities. To solve the headache, people have taken a variety of steps, but the result is not satisfying. Here, one way to solve the problem is to set gas thrifter in vehicle.
Setting gas thrifter in vehicle not only decreases the consumption of gas which is a major source of air pollution but also slows down the cost of possessing a vehicle which makes millaye price lower. Thereby, all vehicles set gas thrifter will make air have a lower carbon dioxide content deriving from burning gas and coal. The less carbon dioxide, the less air pollution. Therefore, through setting gas thrifter, vehicles will bum lower gases, and the problem will partly be solved.
Despite other ways to solve the problem, I think the best way is to set gas thrifter in vehicle for both effect and practice.