Each year the number of cars on roads and streets is becoming larger and larger. Millions of new cars are produced. One out of every six Americans works at putting together the parts of cars, driving trucks, building roads or filling cars with gas. Americans won't live without cars!
Most Americans find it hard to think what life would be without a car. However, some have realised the serious problem of air pollution caused by cars. The polluted air is poisonous and dangerous to health.
One way to reduce the polluted air is to build a new kind of car. Some large car factories are trying to do. But to build a clean car is easier said than done. It develops very slowly.
Another way is to take the place of the car engine (发动机) by something else. Engineers are now working on some new cars. It will take years to develop it.
To prevent the world from being polluted by cars, we'll have to make some changes in the way of life. Americans, for example, have to cut down the number of their cars. They are encouraged to travel and go to work by bike. Riding a bike is thought to help keep the air clean.
But this change does not come easily. A large number of workers may find themselves without jobs if a car factory closes down. And the problem of air pollution would become less important than that of unemployment (失业).
Although cars have brought us a better life, they have also brought us new problems.
