In many big cities in the world, the overuse of cars is thought to be one of the major causes of air pollution. What will cars be 1  in the future?
Some experts think that today's cars are in trouble b   they use too much petrol( 汽油 ). They say the car of the future will be much, much smaller. The car of tomorrow will be m     without a motor or air conditioning. It'll have no radio and no lights. Tomorrow's car will be an o    air car with no doors or windows. It needn't have a pollution control system because it w    use petrol. In fact, this new car will be pushed by the driver's feet. Very few people will be killed in accidents, because the top s        will be five miles per hour. However, we are also warned not to ask for pretty c      , because the cars will come in grey only.
Other car experts do not hold the same idea. They are s        that the future will be happier. They think that all our problems will soon be solved by car companies with the production of the Supercar. Tomorrow's car will be b       , faster, and more comfortable than before. The Supercar will have four rooms, TVs, running water, heat, air conditioning, and maybe a swimming pool. Large families will travel on  1        trips comfortably. If petrol is in short supply ( 供给) , the Supercar will run on water.