Phelps wins 18th gold medal in final race of his career
London Olympics Swimming Men
United States' men's 4 X 100-meter medley relay swimmer Michael Phelps' image is shown on a screen as the relay team sings their national anthem following their gold medal win the at the Aquatics Centre in the Olympic Park during the 2012 Summer Olympics in London, Saturday, Aug. 4, 2012. (AP Photo/Michael Sohn)