Ukrainian Air Force officers attend a graduation ceremony at the National University of Defence of Ukraine in Kiev, April 24, 2015. (Photo by Gleb Garanich/Reuters)

A competitor participates in the Tough Mudder challenge near Henley-on-Thames in southern England May 2, 2015. (Photo by Eddie Keogh/Reuters)

A man rows a boat on the Dal Lake as a woman holds an umbrella during snowfall in Srinagar February 19, 2015. (Photo by Danish Ismail/Reuters)

Young gymnasts practice pull-up on a bar at a gymnasium of a sports school in Jiaxing, Zhejiang province April 11, 2015. (Photo by William Hong/Reuters)

A knight parades in the street during the traditional carnival parade in Cologne, western Germany, Monday, February 16, 2015. (Photo by Martin Meissner/AP Photo)

A frozen public bench is seen next to a lake side due to the heavy wind conditions in Geneva February 8, 2015. (Photo by Pierre Albouy/Reuters)

An Afghan man prepares tea for customers at a roadside tea shop on the outskirts of Jalalabad February 2, 2015. (Photo by Reuters/Parwiz)

Children play football in Bujumbura, Burundi on March 19, 2015. (Photo by Carl de Souza/AFP Photo)