第三部分 概要写作Writing 1阅读下面短文,根据其内容写一篇 60 词左右的内容概要
In 1971, China's first subway line in Beijing was formally put into operation
By December 2017, there were 171 subway lines stretching over 5,083 km in 35 cities on the Chinese mainland
Currently, China has the longest urban railway network in the world, which is predicted to surpass 6,000 km by 2020
The rapid development of China's urban railway system reflects the country's growing economic strength
The system has experienced the fastest growth over the past 15 years due to the investment of wealth accumulated from the reform and opening up in urban infrastructure construction
An urban railway system is expensive to build, with one kilometer of subway costing approximately 700 million yuan (about $110 million)
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