Costumed guests arrive for the “Life Ball” charity event at the Rathaus city hall in Vienna, Austria, 10 June 2017. The 24th Life Ball is a charity fundraiser for HIV and Aids projects. (Photo by Christian Bruna/EPA/EFE)

Couples take part in a competition during a mass wedding of 64 doctoral student couples at Harbin Institute of Technology, a university in Harbin, Heilongjiang province, China, June 4, 2017. (Photo by Reuters/Stringer)

A lemur licks a block of ice containing fruit at Rome's Bioparco zoo, Wednesday, July 5, 2017. Zookeepers at the Bioparco often give animals ice blocks with either fruit or meat on hot summer days. (Photo by Gregorio Borgia/AP Photo)

A woman poses as she beside David Hammons painting on an America flag “Injustice case” at the exhibition Soul Of A Nation, exploring the art made by African American artists between 1963 and 1983, in London, Tuesday, July 11, 2017. The exhibition starts on July 12, 2017 nd ends on Oct.22, 2017. (Photo by Frank Augstein/AP Photo)

People walk on the “Europabruecke” bridge, the world's longest pedestrian suspension bridge with a length of 494m, after the official inauguration of the construction in Randa, Switzerland, 29 July 2017. The bridge is situated on the Europaweg that connects the villages of Zermatt and Graechen. (Photo by Valentin Flauraud/EPA)

Fish are thrown onto a truck during a winter fishing festival held on the frozen Wulungu Lake in Fuhai county, Xinjiang Uighur Autonomous Region, January 18, 2015. (Photo by Reuters/China Daily)

Soldiers stop to buy goods at the main market of Diffa, Niger, March 23, 2015. Diffa is where Nigerien and Chadian troops fighting insurgent group Boko Haram are based at. (Photo by Joe Penney/Reuters)

The Jet Propulsion Lab team's RoboSimian robot turns on a valve at a simulated disaster-response course during day one of the Defense Advanced Research Projects Agency (DARPA) Robotics Challenge finals in Pomona, California, June 5, 2015. (Photo by David McNew/Reuters)