According to the American Automobile(car)Association, since 1964 all cars sold in the United States have been equipped with seat belts (They are also called safety belts) Many studies of car accidents have shown that safety belts can save lives. One study showed that forty percent of those killed in car accidents could have been saved if they have been wearing seat belts. Unfortunately seat belts are worn only by a small number of drivers and passengers _ about fifteen percent in cities and only nine percent in small towns. And safety belt can not protect people who do not wear them. In order to find out what kinds of people do wear seat belts, a study was made in several cities in of the United States. The following facts were learned about those who use their safety belts. 1. They do not smoke while driving. 2. They had more education than less educated people 3. They know some one who was hurt(but not killed) in an accident Advertisements based on these facts have been printed in newspapers and magazines in order to teach people the importance of using seat belt. But these advertisements have not helped much. Some people believe there should be a law ordering drivers and passengers to use safety belts. In Australia, where there is such a law, death in car accidents have reduced to twenty-four percent. One study showed that... Here "study" means  _
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