In this photograph taken on February 18, 2016, Pakistani children ride on swings in the predominantly Pashtun Korangi District of Karachi. In a rundown district of Karachi, Rabia balks at a neighbour's proposal to vaccinate her children, demonstrating one of the biggest hurdles to eradicating polio in Pakistan by the end of the year: confused and frightened parents. (Photo by Asif Hassan/AFP Photo)

An Embraer E-190 E2 aircraft featuring a spray painted tiger's face on the nose of the aircraft is displayed during a media preview of the Singapore Airshow February 4, 2018. (Photo by Edgar Su/Reuters)

A Hindu woman worships the Sun god in the waters of a lake during the religious festival of Chhath Puja in Agartala, India, November 13, 2018. (Photo by Jayanta Dey/Reuters)

Birds sit on the back of a zebra in the Nairobi National Park, near Nairobi, Kenya, November 21, 2018. (Photo by Baz Ratner/Reuters)

Fishermen catch fish at Mao'er lake at the start of winter fishing season which is a local custom to welcome the new year on December 29, 2018 in Huaian, Jiangsu Province of China. (Photo by VCG/VCG via Getty Images)

British fashion model Twiggy plays around on the bumper cars at the Bertram Mills Circus in London, England on January 10, 1967. (Photo by AP Photo)

People take part in a snowball fight in front of the Colosseum covered by snow during a snowfall in Rome, Italy, 26 February 2018. Media reports on 26 February state that extreme cold weather is forecast to hit many parts of Europe with temperatures plummeting to a possible ten year low. (Photo by Angelo Carconi/EPA/EFE)

Afghan female police cadets are seen during their graduation ceremony at Sivas Police Vocational Center Directorate in Sivas, Turkey on March 13, 2018. (Photo by Serhat Zafer/Anadolu Agency/Getty Images)