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Migrant birds fly over the Beidagang Wetland in north China's Tianjin, Dec. 3, 2019. Migratory birds have flocked to the wetland for a winter stopover. (Xinhua/Li Ran)
Migrant birds fly over the Beidagang Wetland in north China's Tianjin, Dec. 3, 2019. Migratory birds have flocked to the wetland for a winter stopover. (Xinhua/Li Ran)