A worker mounts a piece of reflector on China's single-aperture spherical telescope "FAST" in Qiannan of southwest China's Guizhou Province, Nov. 21, 2015. When it is completed in 2016, the five hundred meter aperture spherical telescope (FAST) will be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Xinhua/Jin Liwang)
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