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Novak Djokovic of Serbia attends a "Kids Day" activity ahead of Australian Open 2019 in Melbourne, Australia, Jan. 12, 2019. (Xinhua/Lui Siu Wai)
Novak Djokovic of Serbia attends a "Kids Day" activity ahead of Australian Open 2019 in Melbourne, Australia, Jan. 12, 2019. (Xinhua/Lui Siu Wai)