阅读理解

　　As population increased in large cities in the 19th century, building subway lines was a way to move people from one area of a city to another quickly．The first main subway system, the London Underground, started in 1863 using steam trains．Subway developed quickly in London and the system then had more lines．As of 1896, it strated to use an electrical system．Today's subways around the world now work on electricity．

　　Two of the world's earliest subways were built in Paris and New York．When the Paris Metro opened on July 19,1900 citizens were pround of the beautifully decorated station entrances that have been a landmark ever since．Although the first New York subway consisted of only 14.6 kilometers of track in 1904, today it is the world's largest subway system．

　　Subway trains run in tunnels dug far below the ground．Passengers enter the stations and then take lifts or moving stairs to get on the trains．The deep underground stations of the London and Moscow subways served as safe bomb shelters(防空洞)during World War Ⅱ．Today some cities are building new subways and they dig deep for a different reason．In Athens, Greece, for exmple, the city planners don't want to damage the ancient monument(纪念碑)above the ground．

　　Today, subways are still popular with passengers．The Moscow subway is the busiest in the world with 3.2 billion riders a year．Close behind are subways in Tokyo(2.7billion), Soul(1.6billion), and Mexico City(1.3billion)．Systems that got started early in London, New York and Paris transport millions of riders, and so do subways in Osaka, Hong Kong, and St．Petersburg．

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