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)

Lazar and his sister Andjelka sit by a candle in their home in the eastern Serbian town of Majdanpek, December 4, 2014. Electricity workers in Serbia struggled through snow, ice and treacherous terrain on Thursday to restore electricity to an eastern town left shivering without power, heating or running water for a fourth day. (Photo by Marko Djurica/Reuters)

Supporters of the presidential candidate Muhammadu Buhari and his All Progressive Congress hits another supporter with a motorbike during celebrations in Kano, Nigeria March 31, 2015. (Photo by Goran Tomasevic/Reuters)

A demonstrator is carried during a rally in support of a identity check draft law and against delinquency, in Santiago, Chile April 30, 2016. (Photo by Carlos Vera/Reuters)

Camel racing made its debut in Paxford, Gloucestershire, England yesterday at a point-to-point event on April 22, 2019. Each of the four camels was sponsored by a local pub. (Photo by Paul Nicholls/The Times)

A displaced Yemeni woman from Hodeida fills water containers at a make-shift camp in a village in the northern district of Abs in the country's Hajjah province, on May 9, 2019. The Yemeni conflict has triggered what the United Nations describes as the world's worst humanitarian crisis, with 3.3 million people still displaced and 24.1 million in need of aid. (Photo by Essa Ahmed/AFP Photo)

Rice seedling festival is a traditional folk festival in longji, guangxi, China on June 9, 2019, during grain in ear season. (Photo by Costfoto/Barcroft Media)

Prime Minister Theresa May meets Russian President Vladimir Putin during the G20 summit in Osaka, Japan on June 28, 2019. (Photo by Stefan Rousseau/PA Images via Getty Images)