A calligraphy work is presented at the opening ceremony of the 4th Sino-American Second World War Friendship and Flying Tiger History Conference in Las Vegas, the United States, May 10, 2019. The 4th Sino-American Second World War Friendship and Flying Tiger History Conference opened here Friday to commemorate the American and Chinese heroes and the U.S.-China cooperation during World War II (WWII). (Xinhua/Han Fang)