Students training to be flight attendants hold books on their heads, chopsticks in their mouths, and papers in between their knees, as they take part in a standing posture practice at a vocational school in Shijiazhuang, Hebei province, China May 4, 2017. (Photo by Reuters/Stringer)

Labourers pour molten iron into a container at a foundry in Xiangfan, Hubei province in this July 2, 2010 file photo. Iron ore is enjoying its biggest rally in years, outpacing copper and oil so far in 2016, but still weak forward prices show it may be tough to stretch the bullish outlook. Improving steel prices in top market China are helping fuel iron ore's climb as producers gear up for a seasonal uptick in demand. Yet there is no shortage of doubters who see gains in the bulk commodity as fleeting given a large glut and challenges for China's economy. (Photo by Reuters/Stringer)

A masked reveller poses during the Venice Carnival in Venice, Italy February 12, 2017. (Photo by Tony Gentile/Reuters)

Abbey Clancy attends Warner Music Brits after party on February 22, 2017 in London, England. (Photo by FameFlynet)

A worker manually changes the direction of the bonde, the typical tram line in Santa Teresa neighborhood, using a rope in Rio de Janeiro, Brazil, September 9, 2015. The Santa Teresa bonde, called “Bondinho” in Portuguese, is running with passengers as a part of a test period, after the service was suspended in 2011 following an accident that killed six people, according to residents. (Photo by Pilar Olivares/Reuters)

Tattoo enthusiast Lauren Brock poses to display her body art work during the International London Tattoo Convention in east London, Britain September 26, 2015. (Photo by Neil Hall/Reuters)

Tourists play in front of a 3D painting on the wall of a house in Luoyuan village, Jinhua, Zhejiang province, August 26, 2015. The village hired a team to put on 3D paintings all over the valley as a method to attract tourists and improve the income of local villagers, according to local media. (Photo by Reuters/China Daily)

Graffiti is painted on the bathroom walls at a restaurant in the Williamsburg area of Brooklyn borough in New York, United States, October 1, 2015. Some 2.4 billion people around the world don't have access to decent sanitation and more than a billion are forced to defecate in the open, risking disease and other dangers, according to the United Nations. To mark World Toilet Day on November 19, Reuters photographers captured pictures of toilets in cities, towns and villages around the globe. (Photo by Shannon Stapleton/Reuters)