The mass (大规模) production of cars was developed by Henry Ford in the 1920s and 1930s. At that time, Ford wanted to know how to build cars as quickly and cheaply as possible. It is only recently that people have begun to think about what happens to cars when we no longer use them.
People have become slaves () to the car over the last 60 years. As more new cars are built, the old ones are thrown away to become piles of waste. At the time when people are becoming more "green", that is, paying more attention to the environment, the problem of used cars is now more of an environmental nightmare (噩梦) than ever. The materials used to build cars—mainly steel, plastic, and rubber-are all long-lasting (持久的) and it takes hundreds of years for them to disappear naturally. For example, rubber tires have always been a big environmental problem, and it takes quite a lot of money to make an old rubber tire useful again. A large number of cars began to be produced in the 1920s and 1930s.