Most Americans would find it hard to think that what life   小题1:          

would look like without a car. But, some have realized                         小题2:          

the serious question of the pollution caused by the car.                         小题3:          

The polluted air becomes harmful and dangerous to health             小题4:          

One way to getting rid of the polluted air is to build a             小题5:          

car that doesn’t cause pollution. That is how several of the          小题6:          

large car factories have been tried to do. But to build               小题7:          

a clean car is more easier said than done. Progress in this           小题8:          

field has been slow.

Another way is to take place of the car engine by a                      小题9:          

steam one. Inventors are now working on steam cars as well as

electric cars. Many makers believe that it will spend                 小题10:          

years to develop a practical model that pleased people