单项选择题

Cars are an important 21 of life in the United States. 22 most people feel that they are poor. And 23 if a person is poor he doesn’t feel really poor 24 he has a car.   There are three main reasons the car became so 25 in the United States. 26 of all, the country is a huge one and Americans like to move 27 in it. The car provides the most comfortable and 28 form of transportation. 29 a car people can go any place without spending a lot of money.   The second reason cars are popular is the fact 30 the United States never developed 31 and inexpensive form of public 32 . Long-distance trains have never been 33 common in the United States as they are in other parts of the world. Nowadays there is a good system of air-service 34 planes. But it is 35 expensive to be used frequently.   The third reason is the most important one, though. The American spirit of independence is 36 really made cars popular. Americans don’t like to wait 37 a bus, or a train or even a plane. They don’t like to have to 38 an exact schedule. A car gives them the freedom to schedule 39 time. And this is the freedom that Americans want 40 to have.

A. role
B. part
C.effect
D.basis