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David Marcus, head of Facebook's blockchain subsidiary Calibra, testifies before the Senate Banking, Housing and Urban Affairs Committee on "Examining Facebook's Proposed Digital Currency and Data Privacy Considerations" on Capitol Hill in Washington D.C., the United States, on July 16, 2019. U.S. senators on the Senate Banking Committee used the stage of a hearing Tuesday to grill Facebook executive David Marcus on the controversial Libra cryptocurrency the social network giant plans to unveil next year. (Xinhua/Liu Jie)