WASHINGTON -- The National Zoo has struck a new extension of its longstanding agreement with the Chinese government that will keep the zoo's iconic giant pandas in Washington for another three years.But the agreement also calls for all three pandas — baby Xiao Qi Ji and parents Mei Xiang and Tian Tian — to return to China at the end of 2023.“It will certainly be bittersweet,” said zoo spokeswoman Annalisa Meyer of the eventual departure of the trio.