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Photo taken on Jan. 11, 2018 shows a flag of the United States and a Customs flag at a border crossing station, in Tijuana, Mexico. A long and well-guarded fence with just three gateways divides the two cities, a market of 6.5 million people and an economy that generates 230 billion U.S. dollars a year, according to Mexico's Foreign Ministry. (Xinhua/Xu Rui)