Young man making the O.K. sign. (Photo by George Marks/Retrofile/Getty Images). Circa 1950s

Emma White, of Team Cyclocrossworld, hits the dirt hard during the USA Cycling Cyclo-cross National Championship Elite Women's race at the Valmont Bike Park in Boulder, Colorado, on January 12, 2014. (Photo by Jeremy Papasso/The Daily Camera)

Young men play basketball on an improvised court wedged between a construction site and the shells of once grand colonial homes in Havana, July 20, 2015. As much as the young in Cuba welcome political opening and economic reform, such changes are unlikely to filter down to their lives anytime soon. (Photo by Meridith Kohut/The New York Times)

Rita Ora attends the World Premiere of JEREMY SCOTT: THE PEOPLE'S DESIGNER, presented by The Vladar Company and Quintessentially at the TCL Chinese Theatre on Tuesday, September 8, 2015, in Hollywood, Calif. (Photo by Matt Sayles/Invision for The Vladar Company/AP Images)

A spectator cools herself at a water spraying fan at the Australian Open tennis championships in Melbourne, Australia, Tuesday, January 17, 2017. (Photo by Kin Cheung/AP Photo)

A racegoer is given some water as he lays on the ground following 2017 Stakes Day at Flemington Racecourse on November 11, 2017 in Melbourne, Australia. (Photo by Scott Barbour/Getty Images)

Sun Model students pose for a photo during a training session at the school on March 31, 2014 in Phnom Penh, Cambodia. Having started in August 2010 with only three models, the Sun Model Agency and School is starting to make an impact in the fashion industry in Cambodia. (Photo by Omar Havana/Getty Images)

Members of the Women's Organization to War on Styles (WOW) picket a dress shop in Berkeley, Calif., August 23, 1947, in protest to longer skirts and padded hips. They are the wives of GI students at the University of California. Left to right: Jackie Houser; Wanda Ames; Dorothy Inman; Terry Ligon; Ruth Van Arkel; Carrol Reynolds, and Barbara Carmichael. (Photo by AP Photo)