Twin pandas Meilun and Meihuan play at the Chengdu Research Base of Giant Panda Breeding in Chengdu, southwest China's Sichuan Province, Dec. 6, 2016. Meilun and Meihuan, the twin giant pandas that were born in the United States, traveled back to Chengdu on Nov. 6, 2016 and have been quarantined for one month following the rules of China's animal and plant quarantine law. The twins were born in July, 2013 in Atlanta, U.S.. Their parents, Lunlun and Yangyang, have been living in the United States since 1999. According to the lease agreement between China and U.S., pandas that are born abroad should be returned to China by the age of four. (Xinhua/Xue Yubin)

Twin pandas Meilun and Meihuan play at the Chengdu Research Base of Giant Panda Breeding in Chengdu, southwest China's Sichuan Province, Dec. 6, 2016. Meilun and Meihuan, the twin giant pandas that were born in the United States, traveled back to Chengdu on Nov. 6, 2016 and have been quarantined for one month following the rules of China's animal and plant quarantine law. The twins were born in July, 2013 in Atlanta, U.S.. Their parents, Lunlun and Yangyang, have been living in the United States since 1999. According to the lease agreement between China and U.S., pandas that are born abroad should be returned to China by the age of four. (Xinhua/Xue Yubin)