U.S. Olympic gold medalists Michael Phelps (R) and Adam Nelson fist-bump before they testify to the House Energy and Commerce Subcommittee on Oversight and Investigations during a hearing on "Ways to Improve and Strengthen the International Anti-Doping System" on the Capitol Hill in Washington D.C., the United States, Feb. 28, 2017. (Xinhua/Bao Dandan)
