Factories are usually built  the city to keep the local people from getting harm.

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.

Allan was worried. This was his first time to go travelling 1. He didn't know how to find his seat, 2 he went to the air hostess(空姐) and asked，"Could you help me？I can't find my seat. "The air hostess showed 3 the seat and told him 4 and fasten the seat belt(安全带). She told Allan not to move about when the plane was going up. And she also said that Allan's ears might feel 5 strange，but he didn't need to 6 it because many people felt 7 that. When the plane was flying very high，Allan could stand up and walk around. He could 8 read books，newspapers or see films. The air hostess would 9 food and drinks to him. Allan would enjoy the flight and 10 home soon.

The letter was in my pocket .

Peter did his homework .

His camera is  mine.