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　　It is said that as the population of a city grows, so do its problems．Pollution, too many cars, and crowded streets are just a few of these difficulties．One way to help with these problems is city trains．Trains traveling to different parts of a city mean fewer cars and buses on our roads, cleaner air, and more open streets．In recent years, cities such as Guangzhou, Shenzhen and Shanghai have all built city train lines．

　　The first city train line in China was built in Beijing．The oldest part of the train line, from Beijing Zhan to Ping Guo Yuan was opened in 1969．Its length was 23.6 kilometres．As the city grew after 1980, so did the need for more trains．A newer train line was built to help move people around the city centre．The 16-kilometre-long “circle(环形)line” was finished in 1987．Since that time even more train stations have been built and today the train lines in the city are over 50 kilometres long．

　　For the 2008 Olympic Games, the trains of Beijing will be very important．It is thought that most of the people who go to watch the different sports during the Games will travel using trains．

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