A man takes photos of a model of China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST), the world's largest single-dish radio telescope, at the Third Silk Road International Exposition and the Investment and Trade Forum for Cooperation between East and West China in Xi'an, capital of northwest China's Shaanxi Province, May 11, 2018. The event opened here on Friday. (Xinhua/Shao Rui)