阅读下面短文，根据上下文意义和所给单词首字母，写出空白处适当单词的完全正确形式。（每空一词）

      This summer, the most popular tourist sights in China should be Tibet．Why? Because the Oinghai-Tibet Railway was b 1   the year before last．The Qing-hai-Tibet Railway is the f  2    railway between Tibet and the r 3   of China．It is l,142 kilometers long and is the world’s h 4  railway．About 960 Kilometers of it is over 4,000 meters above sea level．Many people thought it i 5   to build a railway so high．But the railway successful c 6   in the end．

The railway makes the travel c 7   for Tibetans．Most of them can’t a 8   to travel by air．It also brings more tourists to Tibet．It is r 9   that the new railway brings 3,000 to 4,000 tourists to Lasa each day．In Shanghai, one travel agency has worked out a 10-day trip from Shanghai to Lasa for a p 10   of 3,600 yuan．However, this cost may change as the final price for the train has not been decided y 11  ．

A railway trip to Tibet is more c 12    than driving or flying．Each train has special windows to k 13   out ultraviolet（紫外线）light and sandstorms．Thin air m 14   you feel sick．To stop this f 15   happening, the train gives oxygen（氧气）through its air-conditioning system．If you still feel sick, you will find oxygen masks near the seats．