Passengers travel on the London train and underground system during the Christmas party season, December 18, 2015. (Photo by Paul Hackett/Reuters)

People take photos with the skyline of the central business district in Singapore on September 10, 2015. (Photo by Edgar Su/Reuters)

Policemen take pictures of the Soyuz TMA-17M spacecraft while it is transported from an assembling hangar to its launch pad at the Baikonur cosmodrome, Kazakhstan, July 20, 2015. The Soyuz is scheduled to blast off with Kjell Lindgren of the U.S., Kimiya Yui of Japan and Oleg Kononenko of Russia to the International Space Station on July 23, 2015. (Photo by Shamil Zhumatov/Reuters)

People use a board to travel on a flooded street after heavy rainfall in Baghdad, Iraq, October 31 2015. (Photo by Ahmed Saad/Reuters)

Women dressed as nuns pose for pictures during Halloween celebrations in the Shibuya district in Tokyo, Japan October 31, 2015. (Photo by Thomas Peter/Reuters)

Women in costumes walk as they participate in Halloween celebrations in the downtown of Seoul, South Korea, October 31, 2015. (Photo by Kim Hong-Ji/Reuters)

A victim under a blanket lays dead outside the Bataclan theater in Paris, Friday November 13, 2015. (Photo by Jerome Delay/AP Photo)

Labourers unload gravel from a boat docked in Dala township, opposite Yangon city, Myanmar, November 12, 2015. (Photo by Olivia Harris/Reuters)