A worker lays track on the Dunhuang-Golmud Railway in Jiuquan City, northwest China's Gansu Province, June 15, 2019. The last pair of 500-meter-long track were laid on the Dunhuang-Golmud Railway on Saturday, marking the completion of the track-laying work for the railway, which links Dunhuang in northwest China's Gansu Province and Golmud, a city in northwest China's Qinghai Province. (Xinhua/Ma Xiaowei)