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游戏七把数字1,2,3,…,9分别填入图21的9个圈内,要求三角形ABC和三角形DEF的每条边上三个圈内数字之和等于18.
In the game, seven numbers 1, 2, 3, ..., 9 are filled in the 9 circles of Figure 21, and the sum of the numbers in three circles on each side of triangle ABC and triangle DEF is equal to 18.