题目

      Many people believe that Americans love their cars almost more than anything else. It may  be true. From the time youngsters (小孩) become fourteen years old they are likely to dream of  having their own cars. Many young people work after school during their 1st year of high school in  order to buy a car. Learning to drive and getting a driver's license (执照) may be one of the most  exciting times of a young person's life.      People who almost never go to a doctor when they are sick will take their cars to a repairman at the first sign of a problem. Those who 某人在一根装满水的钢管的一端敲击一下后，如果你在钢管很远的另一端，你会听到几次响声？为什么？试试看．