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A U.S. national flag flies at half mast above the to mourn the victims of a mass shooting in a South Florida high school, Washington D.C., the , on Feb. 16, 2018. (Xinhua/Ting Shen)

A U.S. national flag flies at half mast above the to mourn the victims of a mass shooting in a South Florida high school, Washington D.C., the , on Feb. 16, 2018. (Xinhua/Ting Shen)