A bullet train runs on the high-speed railway from Chengdu, capital of southwest China's Sichuan Province, to Xi'an, capital of northwest China's Shaanxi Province, Dec. 6, 2017. The high-speed rail line linking Xi'an and Chengdu went into operation Wednesday, slashing the travel time between the two cities from about 11 hours to just 4. The 658-kilometer new line is China's first rail route running through the Qinling Mountains, the natural boundary between north and south China. (Xinhua/Tang Zhenjiang)