Pilot Akmal Bin Abdul Kahar watches South Korea's Black Eagles aerobatics team perform a manoeuvre during an aerial display at the Singapore Airshow at Changi Exhibition Center February 18, 2016. (Photo by Edgar Su/Reuters)

A migrant boy sits on railway tracks at a train station in Tovarnik, Croatia, September 20, 2015. (Photo by Antonio Bronic/Reuters)

Participants run through the streets of the Back Bay during the 16th annual Santa Speedo Run in Boston, Massachusetts, December 12, 2015. (Photo by Brian Snyder/Reuters)

Revellers react after falling in the mud at Worthy Farm in Somerset during the Glastonbury Festival, Britain, June 26, 2016. (Photo by Stoyan Nenov/Reuters)

A member of Libyan forces allied with the U.N.-backed government fires a weapon on a pickup truck during a battle with Islamic State militants in Giza Bahreya, in Sirte, Libya October 27, 2016. (Photo by Hani Amara/Reuters)

A walker has left a handprint on a snow- covered tree trunk on Grosser Feldberg mountain in the Taunus mountain range, Germany, 16 January 2017. (Photo by Frank Rumpenhorst/DPA)

Kira Walkenhorst of Germany (L) signals as Doaa Elghobashy of Egypt (R) watches during the women's Beach Volleyball preliminary pool D game between Ludwig/Walkenhors of Germany and Elghobashy/Nada of Egypt the Rio 2016 Olympic Games at the Beach Volleyball Arena on Copacabana Beach in Rio de Janeiro, Brazil, 07 August 2016. (Photo by Antonio Lacerda/ANSA)

A weapon is being destroyed during an exercise to disable seized weapons in Caracas, Venezuela August 17, 2016. (Photo by Marco Bello/Reuters)