A Russian trenchmortar crew run to take up a new firing position in the Stalingrad area during the Great Patriotic War. (Photo by Keystone/Getty Images). October 1942

In this Monday, January 18, 2016 photo, Iranian rock climber, Farnaz Esmaeilzadeh, scales a climbing gym in the city of Zanjan, some 330 kilometers (207 miles) west of the capital Tehran, Iran. Esmaeilzadeh, 27, who has been climbing since she was 13, has distinguished herself in international competitions despite the barriers she faces as a female athlete in conservative Iran. (Photo by Ebrahim Noroozi/AP Photo)

Members of the Shanxi Folk Dance and Music Troupe perform during a rehearsal before a show at the Orient Museum in Lisbon February 1, 2016. The show is part of the Chinese New Year Celebrations program of Orient Museum in Lisbon. (Photo by Rafael Marchante/Reuters)

This photo series shows curvy canines and flexible felines participating in a spot of yoga. The shots feature the animals in the likes of the lotus position, balancing on two legs, and stretching in ways that would make the greatest of yoga masters proud. Photographer Dan Borris came up with the idea for the series in 2000, when he was asked by a friend to photograph her in a yoga pose while her dog bothered her. Pictured: Wally. (Photo by Dan Borris/Caters News)

Wildlife photographer Danté Fenolio has headed into areas untouched by sunlight – deep seas, caves and underground – and found creatures that are exploding with colour. Here: The golden harlequin toad has vanished from the wild, and only a small number live on in captivity. A fungus caused them, and many other amphibians, to die out in their home in Central America. (Photo by Danté Fenolio/The Guardian/Johns Hopkins University Press)

Bull riders prepare prior to a bull riding event in Santa Tecla, El Salvador, December 15, 2016. (Photo by Jose Cabezas/Reuters)

Costumed participants take a break during a traditional Perchtenlauf (Perchten parade) in Osterseeon near Munich, Germany, December 17, 2016. (Photo by Michaela Rehle/Reuters)

A woman takes pictures with her mobile phone at a building, which is made by half of a replica of the Qinian Hall of the Temple of the Heaven (R) and half of a western building, at a studio for productions of films and television shows on the outskirts of Shijiazhuang, Hebei province, China, December 3, 2015. (Photo by Reuters/Stringer)