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A worker checks the reflector panels on the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in southwest China's Guizhou Province, Jan. 9, 2020. China completed commissioning of the world's largest and most sensitive radio telescope on Saturday, putting it into formal operation after a productive three-year trial. The telescope will gradually open to astronomers around the globe, providing them with a powerful tool to uncover the mysteries surrounding the genesis and evolutions of the universe. (Xinhua/Liu Xu)