Scientists are trying to design some small cars that may some day take the place of today's big automobiles.If everyone drives such cars in the future,there will be (1)__________in the air.There will also be more space for parking cars in cities,and the streets will be less crowded.Three such cars can fit in the space that is now needed for one car of the usual size.The little cars will cost much less to own and to drive.Driving will be safer, too,as these little cars can go only(2)_______________.
The little cars of the future will be fine for getting around the city,but they will not be useful for long trips.Little cars which are powered by gasoline will go (3)_____________ kilometersbefore needing to stop for more gasoline.If big cars are still used along with the small ones,two sets of roads will be needed in the future.Some roads will be used for the big,fast cars and other roads will be needed for the slower, small ones.
