【正确答案】
A
【答案解析】[听力原文]17-20
The territorial growth in the United States was followed by great industrial expansion. The country was rich in natural resources. A constant flow of immigration provided the labor force necessary to develop these resources. New industries were started. Chicago, St. Louis, and Detroit grew from small towns to large cities. The Unites States became the greatest industrial country in the world.
Detroit's growth has been typical of these new American cities. Situated on the Detroit River close to the Great Lakes, it had the geographical advantages necessary for industrial growth. Factories for manufacture of bicycles and wagon bodies were established there. With the coming of the automobile, these factories were convened into automobile plants. The American system of mass production was introduced. The industry grew and Detroit grew with it.
Detroit today is the fifth largest city in the Unites States. Four Detroit automobile companies produce 96 percent of all American cars. Twenty thousand of these cars roll off Detroit assembly lines each day. Some of the factories there never stop. They have three groups or "shifts" of workers. Each shift works eight hours and is relieved by a new shift, making all together a twenty-four-hour day. So it is that Detroit has been called "The City of Three Shifts." As a result, in the Ford plant it is possible to build an entire car in less than twenty-eight hours. In little more than a day, pure iron ore can be converted into a shiny new car of the latest model.
[解析] 本题考查主旨大意。本文讲述了底特律各大汽车制造厂每天三班二十四小时不间断地生产汽车，产量占到美国汽车产量的96%。所以[A]是最佳答案。