A、When they don’t have a car. B、When they live in a huge country. C、When they don’t use planes. D、when they have a car. A本题关键句为“

Cars are an important part of life in the United States. (29) Without a car most people feel that they are poor. And even if a person is poor he doesn’t feel really poor when he has a car. The car made the United States a nation on wheels. And it helped make the United States what it is today. There are three reasons the car became so popular in the United States. First of all the country is a huge one and Americans like to move around in it. The car provides the most comfortable and cheapest form of transportation. With a car people can go any place without spending a lot of money. The second reason that cars are popular is the fact that the United States never really developed an efficient and inexpensive form of public transportation. Long-distance trains have never been as common in the United States as they are in other parts of the world. Nowadays there is a good system of air-service provided by planes. But it is too expensive to be used frequently. (30) The third reason is the most important one, though. The American spirit of independence is what really made cars popular. Americans don’t like to wait for a bus, or a train or even a plane. They don’t like to have to follow an exact schedule. A car gives them the freedom to schedule their own time. And this is the freedom that Americans want most to have. (31) The gas shortage has caused a big problem for Americans. But the answer will not be a bigger system of public transportation. The real solution will have to be a new kind of car, which does not use so much gas.