A staff member feeds giant panda cub Lu Lu at the Shaanxi Rare Wild Animals Rescue and Breeding Research Center in northwest China's Shaanxi Province, Sept. 7, 2018. Four giant panda cubs, born at the center in 2017, grow well now. (Xinhua/Zhang Bowen)

Giant panda cubs Lu Lu (L) and Qiang Sheng play at the Shaanxi Rare Wild Animals Rescue and Breeding Research Center in northwest China's Shaanxi Province, Sept. 7, 2018. Four giant panda cubs, born at the center in 2017, grow well now. (Xinhua/Zhang Bowen)

Four giant panda cubs play at the Shaanxi Rare Wild Animals Rescue and Breeding Research Center in northwest China's Shaanxi Province, Sept. 7, 2018. Four giant panda cubs, born at the center in 2017, grow well now. (Xinhua/Zhang Bowen)

Giant panda cub Shan Zai plays at the Shaanxi Rare Wild Animals Rescue and Breeding Research Center in northwest China's Shaanxi Province, Sept. 7, 2018. Four giant panda cubs, born at the center in 2017, grow well now. (Xinhua/Zhang Bowen)

Four giant panda cubs play at the Shaanxi Rare Wild Animals Rescue and Breeding Research Center in northwest China's Shaanxi Province, Sept. 7, 2018. Four giant panda cubs, born at the center in 2017, grow well now. (Xinhua/Zhang Bowen)