Romanian military doctors and medical students sit on a bus behind steamy windows before the National Day parade in Bucharest, Romania, Thursday, December 1, 2016. Military planes and helicopters flew over the Romanian capital Thursday as thousands turned out to celebrate the national day, marking the date when the country reunified with Transylvania in 1918. (Photo by Vadim Ghirda/AP Photo)

A man dressed as Father Frost, Russian equivalent of Santa Claus, sits by the fire with a reindeer Yakut, marking winter solstice at the Royev Ruchey Park of Flora and Fauna in the Siberian Taiga wood in the suburbs of Krasnoyarsk, Russia, December 21, 2016. (Photo by Ilya Naymushin/Reuters)

Participants take part in the annual Great Spitalfields Pancake Race in aid of London's Air Ambulance in London, Britain February 9, 2016. (Photo by Stefan Wermuth/Reuters)

A keeper feeds a four-week-old jaguar while presenting it to the media, at a zoo in Ciudad Juarez, Mexico, October 14, 2015. (Photo by Jose Luis Gonzalez/Reuters)

Fireworks explode over Elizabeth Tower housing the Big Ben clock in London. (Photo by Kirsty Wigglesworth/Associated Press)

View of the Villarrica volcano taken from Pucon, some 800 kilometres south of Santiago, showing signs of activity on December 06, 2017. (Photo by Christian Miranda/AFP Photo)

A woman walks past a stall at a market in Banjul, Gambia December 15, 2016. (Photo by Afolabi Sotunde/Reuters)

Film actress Audrey Hepburn (1929–1993) on a film set with her pet poodle, circa 1960. (Photo by Hulton Archive/Getty Images)