综合题。结合听力全文可知，这篇文章主要是讲汽车在美国是如何重要，文章还简单介绍了一下其发展概况，所以本题答案为Cars。
【录音原文】
　　Americans depend on their cars more than any other people. The family car has been a common thing in the early 20th century, and it has changed American life. Many people have moved outside of the large cities to the suburbs. Some Americans spend two hours a day or more in their cars going to work and back home. Cars have become the means of transportation for most Americans when they go shopping and even go on vacations. In the past, Americans liked big cars, and the gas wasn’t expensive. However, the price of gas has greatly increased in recent years. Smaller cars and foreign cars have become very popular. That’s why Japanese and German cars sell well in the US.
Q11: When did the family car become common in America?
Q12: Why do more Americans have to drive to work?
Q13: Why do people like smaller cars now?
Q14: How popular are Japanese and German cars in the U.S.?
Q15: What does the speaker mainly talk about?