Meng Meng, one of two Chinese pandas, receives a birthday cake to mark its fourth birthday in the enclosure at the zoo in Berlin, on July 10, 2017. (Photo/VCG)

Panda Meng Meng receives a birthday cake to mark its fourth birthday in the enclosure at the zoo in Berlin, on July 10, 2017. (Photo/VCG)

Chinese panda Meng Meng is seen in its enclosure during the visit of German Chancellor Angela Merkel and Chinese President Xi Jinping at the Zoo in Berlin, Germany, July 5, 2017. (Photo/Agencies)