Xu Caiyun patrols the Guanjiao tunnel, in a section of the Qinghai-Tibet Railway in Haixi Mongol and Tibet autonomous prefecture in Northwest China's Qinghai province, June 25, 2011. The 44-year-old Xu has been doing maintenance work for 17 year under the harsh conditions of the tunnel, where icicles and frost are common. The 4-kilometer Guanjiao tunnel, at an elevation of 3,700 meters, is the longest tunnel in the world on a plateau. [Photo/Xinhua]
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