14 week-old twin polar bear cubs play during their first presentation to the media in Hellabrunn zoo on March 19, 2014 in Munich, Germany. The male and female twins were born on December 9, 2013 in the zoo. (Photo by Alexandra Beier/Getty Images)

In this undated handout photograph from the “Inside Out Project”, a poster bearing the image of a Pakistani girl whose parents, lawyers say, were killed in a drone strike, lies in a field at an undisclosed location in the northwestern Khyber-Pakhtunkhwa province. A group of artists in Pakistan are hoping to generate “empathy” among US drone operators by placing giant posters of children in the country's troubled tribal regions. (Photo by AFP Photo)

A child coughs as migrants and refugees run away after Macedonian police fired tear gas at hundreds of Iraqi and Syrian migrants who tried to break through the Greek border fence in Idomeni, on February 29, 2016. Greek police said more than 6,000 people were massed at the border, in a buildup triggered by Austria and Balkan states capping the numbers of migrants entering their territory. (Photo by Louisa Gouliamaki/AFP Photo)

A man lights up his cigarette with the flames of a bus burned by anti-government demonstrators during a protest against the constitutional amendment PEC 55, which limits public spending, in front of Brazil's National Congress in Brasilia, Brazil December 13, 2016. (Photo by Adriano Machado/Reuters)

Irene Bowker, 88 years old at the Punk Rebellion festival at The Winter Gardens, talks to a woman with a tatooed head and mohican haircut in Blackpool, Lancashire, UK on August 6, 2015. A clash cultures at the famous seaside town of Blackpool as punks attending the annual Rebellion festival at the Winter Gardens come shoulder to shoulder with traditional holidaymakers. (Photo by MediaWorldImages/Alamy Stock Photo)

A woman lies face-down on the floor where other race-goers are standing on 2017 Derby Day at Flemington Racecourse on November 4, 2017 in Melbourne, Australia. (Photo by Splash News and Pictures)

A Macedonian police officer hits a stranded migrant attempting to cross the Greek-Macedonian border, near Gevgelija, Macedonia December 2, 2015. Picture taken from the Greek side of the border. (Photo by Alexandros Avramidis/Reuters)

Graffiti saying “justice” partially seen above flood waters in Asuncion, December 27, 2015. More than 100,000 people have had to evacuate from their homes in the bordering areas of Paraguay, Uruguay, Brazil and Argentina due to severe flooding in the wake of heavy summer rains brought on by El Nino, authorities said on Saturday. (Photo by Jorge Adorno/Reuters)