Hotel staff practice self-defence skills after a training session given by team member of Special Weapons and Tactics (SWAT) team, in Hangzhou, Zhejiang province, April 7, 2016. (Photo by Reuters/Stringer)

Hospitality staff members laugh as they stand on Tiananmen Square before the closing ceremony of China's 19th Party Congress at the Great Hall of the People in Beijing, Tuesday, October 24, 2017. The ruling Communist Party on Tuesday formally lifted Xi Jinping's status to China's most powerful ruler in decades, setting the stage for the authoritarian leader to tighten his grip over the country while pursuing an increasingly muscular foreign policy and military expansion. (Photo by Mark Schiefelbein/AP Photo)

Four-month-old fox cubs squaring up to each other in Walthamstow, England on August 7, 2015. (Photo by Greg Morgan/Barcroft Media)

An undercover police officer, who had been marching with anti-police demonstrators, aims his gun at protesters after some in the crowd attacked him and his partner in Oakland, California December 10, 2014. Police said more than 100 demonstrators marched in Berkeley, California, which has a history of social activism. Under cloudy skies, turnout was smaller than earlier in the week, when demonstrators in the area threw rocks at police and shut down a major freeway. (Photo by Noah Berger/Reuters)

This is the incredible moment a fierce lightning bolt crashed against the Grand Canyon illuminating the steep canyon walls. Shrouded in darkness, the breath-taking landscape was shocked into life as mother nature sent the bolt storming down to Earth. As it cracked against the rocks the bright blue bolt illuminated the South Rim of the canyon, considered one of the Seven Natural Wonders of the World. With just the Desert View Watchtower in the foreground, the lightning was perfectly framed by the canyon which is located in Arizona, USA. (Photo by Travis Roe/U.S. Dept. of the Interior/Caters News)

Afghan firefighters spray water on a U.S. armoured vehicle after a suicide attack on the outskirts of Jalalabad, January 5, 2015. A suicide attacker targeted a U.S. convoy on the outskirts of Jalalabad on Monday but so far no causalities have been reported yet, provincial spokesman Ahmadzia Abdulzai said. (Photo by Reuters/Parwiz)

A boy tumbles as he plays soccer on the streets of the Khayelitsha township in Cape Town, December 3, 2009. (Photo by Kai Pfaffenbach/Reuters)

A view of an entrance to the concrete case surrounding the pressure vessel of the reactor is seen inside the decommissioned Unit Six of the Greifswald nuclear power station outside Lubmin August 5, 2014. Unit Six was a part of East Germany's largest nuclear power plant that was nearly completed in 1990, when the country's re-unification halted construction. (Photo by Thomas Peter/Reuters)