Mei Xiang, one of two giant pandas at Smithsonian's National Zoo in Washington, D.C., gave birth to twin cubs hours apart Saturday. They mark her second and third cubs in two years, following the birth of Bao Bao in August 2013. The pandas, which are not yet named, must be reared apart following protocol, but both twins will get time with their mother. The cubs will be returned to China four years after birth.

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