A child poses for photos with giant panda toys at the Calgary Zoo in Calgary, Canada, on July 16, 2018. After moving to the Calgary Zoo from Toronto in March, giant panda cubs Jia Panpan, Jia Yueyue, their mother Er Shun and male adult giant panda Da Mao are expected to attract lots of visitors in the summer holiday. (Xinhua/Zou Zheng)

People look at a giant panda at Panda Passage of the Calgary Zoo in Calgary, Canada, on July 16, 2018. After moving to the Calgary Zoo from Toronto in March, giant panda cubs Jia Panpan, Jia Yueyue, their mother Er Shun and male adult giant panda Da Mao are expected to attract lots of visitors in the summer holiday. (Xinhua/Zou Zheng)

Photo taken on July 16, 2018 shows the entrance of Panda Passage at the Calgary Zoo in Calgary, Canada. After moving to the Calgary Zoo from Toronto in March, giant panda cubs Jia Panpan, Jia Yueyue, their mother Er Shun and male adult giant panda Da Mao are expected to attract lots of visitors in the summer holiday. (Xinhua/Zou Zheng)

People visit Panda Passage at the Calgary Zoo in Calgary, Canada, on July 16, 2018. After moving to the Calgary Zoo from Toronto in March, giant panda cubs Jia Panpan, Jia Yueyue, their mother Er Shun and male adult giant panda Da Mao are expected to attract lots of visitors in the summer holiday. (Xinhua/Zou Zheng)

A girl visits an exhibition of giant panda at the Calgary Zoo in Calgary, Canada, on July 16, 2018. After moving to the Calgary Zoo from Toronto in March, giant panda cubs Jia Panpan, Jia Yueyue, their mother Er Shun and male adult giant panda Da Mao are expected to attract lots of visitors in the summer holiday. (Xinhua/Zou Zheng)

People visit Panda Passage at the Calgary Zoo in Calgary, Canada, on July 16, 2018. After moving to the Calgary Zoo from Toronto in March, giant panda cubs Jia Panpan, Jia Yueyue, their mother Er Shun and male adult giant panda Da Mao are expected to attract lots of visitors in the summer holiday. (Xinhua/Zou Zheng)