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閱讀理解。
Beijing-Shanghai Railway was completed in 1968．The line runs 1,462 km between China's two main cities and passes through five provinces and the city of Tianjin．
Since opening,it has been one of the busiest routes in our country．The Beijing-Shanghai route is now served by 10 trains a day,five of which are non-stop．The journey time is just under 12 hours．
Now trains are allowed to travel at 250 kph(kilo-metres per hour)and the journey time is only 10 hours．
With the sixth railway speedup,China has joined the ranks(行列)of countries with high-Speed rail services．Trains are able to run at speed of 200 kph on some 6,003 km of track(軌道),and on some sections,the highest speed can increase t0 250 kph．The 6,003 km of track serves both high-speed passenger trains and low-speed cargo(貨物)trains．
Railway operators have to deal with the problem of the speed gap(差距)between the two kinds of trains to make sure they both run safely．
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