A German Air Force Officer sits astride a dead boar outside a house where he is stationed near the Western Front, in this 1918 handout picture. This picture is part of a previously unpublished set of World War One (WWI) images from a private collection. The pictures offer an unusual view of varied and contrasting aspects of the conflict, from high tech artillery to mobile pigeon lofts, and from officers partying in their headquarters to the grim reality of life and death in the trenches. The year 2014 marks the centenary of the start of the war. (Photo by Reuters/Archive of Modern Conflict London)

A street cleaner demonstrates his martial arts skills in front of a closed shop near Beijing's Tiananmen Square September 2, 2015 as the capital prepares for tomorrow's parade. (Photo by Damir Sagolj/Reuters)

Revelers, covered in coloured powder, celebrate, during a Holi Run Festival in Madrid, Spain, Sunday, April 12, 2015. Thousands of revelers took part in the festival that includes a mini marathon. The festivals are fashioned after the Hindu spring festival Holi, which is mainly celebrated in the north and east of India. (Photo by Andres Kudacki/AP Photo)

Eurocopter's X³ high-speed hybrid helicopter demonstrator performs, September 6, 2010. The Eurocopter X³ (X-Cubed) is an experimental high-speed compound helicopter developed by Eurocopter (now Airbus Helicopters). A technology demonstration platform for Eurocopter “high-speed, long-range hybrid helicopter” or H³ concept, the X³ achieved 255 knots in level flight on 7 June 2013, setting an unofficial speed record for a helicopter. (Photo by Reuters/HO/Eurocopter/Penna)

Recording artist Ariana Grande performs onstage during the 2014 iHeartRadio Music Festival at the MGM Grand Garden Arena on September 19, 2014 in Las Vegas, Nevada. (Photo by Kevin Winter/Getty Images for iHeartMedia)

Radin the Sunda pangolin hitches a ride on Nita as their keeper looks on. The elusive and nocturnal Sunda pangolin produces only one or two offspring a year and Radin is the third pangolin baby born in Night Safari since 2011. (Photo by Wildlife Reserves Singapore)

A dancer poses for a photograph as part of the “Dance as Art” photo project in Times Square in New York, on September 22, 2014. (Photo by Carlo Allegri/Reuters)

A protestor makes a selfie in front of a burning car during a national trade union demonstration in Brussels, Thursday November 6, 2014. Tens of thousands of demonstrators are converging on the Belgian capital to protest government policies that will extend the pension age, contain wages and cut into public services. (Photo by Geert Vanden Wijngaert/AP Photo)