Giant panda Tian Tian celebrates 21st birthday in Washington D.C.

Zookeepers bring out the birthday cake for giant panda Tian Tian at the Smithsonian's National Zoo in Washington D.C., the United States, on Aug. 27, 2018. The zoo held a celebration on Monday for giant panda Tian Tian's 21st birthday. [Photo: Xinhua]