First graders of a cadet's lyceum attend a ceremony to mark the start of the new school year in Kiev, Ukraine, September 1, 2015. September 1 marks the start of a new academic year for students in Ukraine.(Photo by Valentyn Ogirenko/Reuters)

Japan's delegation gather to sign the formal surrender document on the U.S. Navy battleship USS Missouri in Tokyo Bay in a September 2, 1945 file photo. (Photo by Reuters/US Navy)

The sun rises over St Mary's Lighthouse in Whitley Bay on the Northumberland coast as a flock of Lapwing seabirds fly past on Wednesday, September 30, 2015. (Photo by Owen Humphreys/PA Wire)

A protestor opposed to U.S. Republican presidential candidate Donald Trump's stance on immigration clashes with Trump supporters at a rally in Norcross, Georgia October 10, 2015. (Photo by Tami Chappell/Reuters)

A girl reacts as she receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)

A man smiles as he carries firewood he bought on a street amid ongoing fuel and cooking gas shortages in Yemen's capital Sanaa December 2, 2015. (Photo by Khaled Abdullah/Reuters)

A tribesman loyal to the Houthi movement carries his rifle as he leaves a gathering held to show support for the group, in Yemen's capital Sanaa December 15, 2015. (Photo by Khaled Abdullah/Reuters)

Refugees disembark and make their way to a camp at a hotel touted as the world's most northerly ski resort in Riksgransen, Sweden, December 15, 2015. (Photo by Ints Kalnins/Reuters)