Ariana Grande performs at Z100's Jingle Ball in Manhattan, New York, U.S., December 9, 2016. (Photo by Andrew Kelly/Reuters)

Passengers wear no trousers as they ride the London Underground in London, Britain, 07 January 2018. The No Pants Subway Ride is an global annual event where people take the public transport while they are not wearing trousers to surprise other passengers. This event takes place on the first Sunday of every year in the world's major cities. (Photo by Tolga Akmen/EPA/EFE/Rex Features/Shutterstock)

A passenger takes off his pants as others not wearing pants dance while waiting for a subway train during the “No Pants Subway Ride” in Mexico City, Mexico, February 21, 2016. The event is an annual flash mob and occurs in different cities around the world, according to its organisers. (Photo by Carlos Jasso/Reuters)

Three Chinese soldiers at the time of a civil war in China. (Photo by General Photographic Agency/Getty Images). 1922

An aerial view of the lava erupting during volcanic eruption in September, in Bardarbunga, Iceland. Lava spews out from craters as molten rock flows into a river down the Bardarbunga volcano in Iceland. The dramatic pictures of the Holuhraun eruption were taken from an altitude of 50-500m on September 5-9 by Örvar Atli Þorgeirsson at twilight and with the stunning Aurora Borealis in the background. (Photo by Örvar Atli Þorgeirsson/Barcroft Media)

Julian, left, is photographed by his mother with friend Gianluca, right, under water at a public pool in Gelsenkirchen, Germany, on a hot Friday, July 3, 2015. Germany faces a heat wave with temperatures up to 38 degrees Celsius (100 degrees Fahrenheit) at the weekend. (Photo by Martin Meissner/AP Photo)

Members of the Communist New Fourth Army on parade. Note how the modern equipment contrasts with the shoeless soldiers in the foreground. (Photo by Hulton Archive/Getty Images). 6th July 1946