完形填空：从各题所给的四个选项中选出最佳答案。（共15小题；计15分） The United States is full of automobiles (机动车). There are still many families without cars. But some Families have two or more cars. However,cars are used for more than pleasure. They are apart of life. Cars are used for. They are driven to offices and factories by workers who have no other way totheir jobs. When salesmen are sent toparts of the city, they have to drive in order totheir products. Farmers have to drive into the city in order to shop for necessities. Sometimes, small children must be driven to. In some cities, school buses are used only when childrenmore than a mile from the school. When the children are too to walk that far, their parents takedriving them to school. One11drives on Mondays, taking her children and the neighbors' children as well. Another mother drives on Tuesdays, another on Wednesdays and so on. This isforming a car pool (拼车). Working people also form car pools, with three or four people taking turns driving to the placethey work. More car pools should be formed in order to putcars on the road and to use less oil. is a great problem, and so is the traffic in and around cities. Too many cars are being driven. Something should be done about the use of cars.