​Giant pandas Chengjiu and Shuanghao eat bamboo and a special panda birthday cake during celebrations for their fourth birthday at Hangzhou Zoo in east China's Zhejiang Province on Tuesday, July 31, 2018. [Photo: IC]

​A special panda-friendly birthday cake was made for giant pandas Chengjiu and Shuanghao. The pair celebrated their fourth birthday at Hangzhou Zoo in east China's Zhejiang Province on Tuesday, July 31, 2018 .[Photo: IC]

​Giant pandas Chengjiu and Shuanghao playing during celebrations for their fourth birthday at Hangzhou Zoo in east China's Zhejiang Province on Tuesday, July 31, 2018. [Photo: IC]

​Giant pandas Chengjiu and Shuanghao eat bamboo and a special panda birthday cake during celebrations for their fourth birthday at Hangzhou Zoo in east China's Zhejiang Province on Tuesday, July 31, 2018. [Photo: IC]