(L-R) Courtney Okolo, Natasha Hastings, Phyllis Francis and Allyson Felix of the United States of America react after the women's 4x400m relay final of Athletcis at the 2016 Rio Olympic Games in Rio de Janeiro, Brazil, on Aug. 20, 2016. The U.S. team won the gold medal. (Xinhua/Wang Lili)