7.Xi'an-Chengdu high-speed trains

A bullet train runs through Zhaojialing tunnel during a test run in northwest China's Shaanxi Province, Nov. 22, 2017. High-speed trains linking Xi'an, capital of Shaanxi Province, and Chengdu, capital of Sichuan Province, began operation on Dec. 6, 2017. (Xinhua/Tao Ming)

A bullet train runs through Zhaojialing tunnel during a test run in northwest China's Shaanxi Province, Nov. 22, 2017. High-speed trains linking Xi'an, capital of Shaanxi Province, and Chengdu, capital of Sichuan Province, began operation on Dec. 6, 2017. (Xinhua/Tao Ming)