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)

A student, wearing a traditional costume and headdress, stands in line for interviews during a recruitment held by an airline company, hoping to stand out from more than 500 candidates for airline stewardess positions, in Chengdu, Sichuan Province, China, May 27, 2016. (Photo by Reuters/Stringer)

People commute during a heavy rain shower in Chandigarh, India, June 22, 2016. (Photo by Ajay Verma/Reuters)

A lioness drinks after being fed by senior keeper Glynn Hennessy at ZSL London Zoo on August 10, 2016 in London, England. Today marks World Lion Day which highlights the first global campaign to celebrate the importance and plight of lions worldwide. (Photo by Carl Court/Getty Images)

Saintsetseg Jambaldorj, a member of the Tsaatan ethnic minority, one of the last remaining groups of nomadic reindeer herders in East Taiga, Mongolia, wearing a traditional deel, on July 5, 2016. (Photo by Madoka Ikegami/Barcroft Images)

Students celebrate their A-level results at King Edward VI High School for Girls in Birmingham, England on August 18, 2016. The proportion of top grades achieved by A-level students across the UK has fallen for a fifth year in a row, and girls have caught up with boys in attaining A* grades. (Photo by Joe Giddens/PA Wire)

Te Matatini Kapa Haka Aotearoa perform the Haka at the Edinburgh Festival Fringe on the Royal Mile on August 14, 2014 in Edinburgh, Scotland. The largest performing arts festival in the world, this years festival hosts more than 3,000 shows in nearly 300 venues across the city. (Photo by Jeff J. Mitchell/Getty Images)

Russian servicewomen march at Red Square during the Victory Day military parade in Moscow on May 9, 2017. Russia marks the 72nd anniversary of the Soviet Union's victory over Nazi Germany in World War Two. (Photo by Kirill Kudryavtsev/AFP Photo)