Photo taken on Dec. 3, 2016 shows a giant karst sinkhole in Zhenba County of Hanzhong City, northwest China's Shaanxi Province. High-speed trains linking Xi'an, capital of Shaanxi Province, and Chengdu, capital of Sichuan Province, will begin operation on Dec. 6, authorities said Sunday. With a new train diagram to be put into operation at the end of this year, travel time between the two cities will be slashed by about 7 hours to just 3 hours and 27 minutes. The train service will provide a new choice for tourists to the two provinces. (Xinhua/Tao Ming)