A Mark IV tank, part of the parade at the Lord Mayor's Show in London. (Photo by Topical Press Agency/Getty Images). November 1917

In this picture taken Thursday, April 14, 2016, a Syrian man carries a carpet as walk through a devastated part of the town of Palmyra as families load their belongings onto a bus in the central Homs province, Syria. Thousands of residents of this ancient town who fled Islamic State rule are returning briefly to check on their homes and salvage what they can – some carpets, blankets, a fridge or a few family mementos. There is no water or electricity in the town, and it will be at least few months before anyone can return to stay. (Photo by Hassan Ammar/AP Photo)

Star trails form over the Memorial House of the Bulgarian Communist Party on mount Buzludzha in this long exposure picture taken on September 12, 2014. The monument was officially opened in 1981 by the Bulgarian Communist regime to mark 100 years of the set up of an organised Socialist movement, a predecessor of the Bulgarian Communist Party. The monument, no longer maintained by the Bulgarian government after the fall of the Communist regime in 1989, is now abandoned and vandalized. (Photo by Stoyan Nenov/Reuters)

Santa Claus greets a child during a visit to residents of the slum of Petare in Caracas, Venezuela, December 11, 2016. (Photo by Ueslei Marcelino/Reuters)

In this September 10, 1977, file photo, from left, Hua Guofeng, Chinese Communist Party (CCP) chairman and Mao Zedong's immediate successor; Ye Jianying, CCP vice chairman and future ceremonial head of state; Deng Xiaoping, no formal titles at the time but soon to emerge as paramount leader during the reform era; Li Xiannian, CCP vice chairman and future president; Wang Dongxing, head of the leadership bodyguard unit who helped topple the Gang of Four, view the body of later Chinese leader Mao Zedong in Beijing. (Photo via AP Photo)

American soldiers leaping from an armoured personnel carrier during exercises in Korea, 17th March 1954. (Photo by Three Lions)

Tacos of Cochinita Pibil, a popular dish from Yucatan, are seen during an attempt to break the Guinness World Record for the world's longest taco in Guadalajara February 15, 2015. Guadalajara broke the Guinness record for the longest taco of cochinita pibil, with a length of 2.5 kilometers, as part of the COME gastronomy festival, local media reported. For the preparation of the traditional dish, the chefs used 4 tons of pork, 36,000 tortillas and spices for 325 taco servings. (Photo by Alejandro Acosta/Reuters)