[填空题] Cars are an important 【B1】______ of life in the United States. 【B2】______ most people feel that they are poor. And 【B3】______ if a person is poor he doesn’’t feel really poor 【B4】______ he has a car. There are three main reasons the car become so 【B5】______ in the United States. 【B6】 ______ of all the country is a huge one and Americans like to move 【B7】______ in it. The car provides the most comfortable and 【B8】______ form of transportation. 【B9】______ a car people can go any place without spending a lot of money. The second reason cars are popular is the fact 【B10】______ the United States never developed 【B11】______ and inexpensive form of public 【B12】______. Long distance trains have never been 【B13】______ common the United States as they are in other parts of the world. Nowadays there is good system of air service 【B14】______ planes. But it is 【B15】______ expensive to be used frequently. The third reason is the most important one, though. The American spirit o
A. A．although
B．when
C．whether
D．but