A visitor takes photos of the panda cubs during their first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)

Yuan Yuan, one of the twin panda cubs, makes its first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)

Yuan Yuan, one of the twin panda cubs, makes its first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)

Three panda cubs including a pair of twins make their first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)

Three panda cubs including a pair of twins make their first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)

Three panda cubs including a pair of twins make their first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)

Yuan Yuan, one of the twin panda cubs, makes its first appearance at the Qinling Research Base of Giant Panda Breeding of Shaanxi Academy of Forestry in Xi'an, northwest China's Shaanxi Province, Nov. 11, 2019. (Xinhua/Li Yibo)