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). A city without economic strength cannot develop such an expensive system.The progress in urban railway construction technologies has also contributed to the fast expansion of the infrastructure. Subway construction involves building underground tunnels, laying rails, manufacturing trains and the operation and management of subways. It is a systematic project which not only covers traditional infrastructure building but also modern electronics and information technology. China's railway construction technologies are the best in the world, with Chinese subway trains now exported to developed countries including the United States.The expansion of Chinese cities has made it necessary to develop urban railway systems. Since the start of the reform and opening up, a large number of people have migrated to cities and the number of private cars has increased dramatically, resulting in serious traffic congestion. Building subways has ...
