Fifth-grade students of the General Yermolov Cadet School get prepared before their first military tactical exercise on the ground, which includes radiation resistance classes, forest survival studies and other activities, in Stavropol, Russia, September 10, 2016. Picture taken September 10, 2016. (Photo by Eduard Korniyenko/Reuters)

A women wearing a mask to protect from extreme smog visits the Tiananmen Gate in Beijing December 8, 2015 as China's capital issues its first ever "red alert" for pollution. (Photo by Damir Sagolj/Reuters)

Front end detail of the Hyundai Santa Cruz crossover concept truck as it is displayed during the first press preview day of the North American International Auto Show in Detroit, Michigan January 12, 2015. (Photo by Rebecca Cook/Reuters)

2000 attended a welcome party at TigerTiger Manchester which was the first event in set of big club night for new students to Manchester and Salford universities in Manchester, UK on September 19, 2016. This year, university bosses have stepped up security in Manchester. (Photo by Jordan Sinclair/UK News Pictures)

Marco Antonio Eguchi of Brazil gets bucked off of Bottoms Up in the first round of the PBR Frontier Communications Iron Cowboy at AT& T Stadium on February 18, 2017 in Arlington, Texas. (Photo by Tom Pennington/Getty Images)

South Korea's Lee Dae-ho is hit by a pitch off Taiwan's pitcher Pan Wei-lun during the second inning of their first round game of the World Baseball Classic at Gocheok Sky Dome in Seoul, South Korea, Thursday, March 9, 2017. (Photo by Ahn Young-joon/AP Photo)

The car driven by Scott Dixon, of New Zealand, goes over the top of Jay Howard, of England, in the first turn during the running of the Indianapolis 500 auto race at Indianapolis Motor Speedway, Sunday, May 28, 2017, in Indianapolis. (Photo by Marty Seppala/AP Photo)

Former Olympic gymnast Nastia Liukin performs a flip while throwing the ceremonial first pitch during a baseball game between the Los Angeles Angels and the Tampa Bay Rays, Friday, July 14, 2017, in Anaheim, Calif. (Photo by Jae C. Hong/AP Photo)