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Lassina Zerbo (2nd L), executive secretary of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), visits a radionuclide station in Guangzhou, south China's Guangdong Province, Jan. 30, 2018. Four China-hosted nuclear activity monitoring stations were presented with certificates by CTBTO Tuesday in Guangzhou. (Xinhua/Liang Xu)