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)

An Afghan girl harvests Cotton buds at a field on the outskirts of Balkh province, Afghanistan, November 15, 2014. (Photo by Sayed Mustafa/EPA)

Kevin and Merith Starren have their picture taken by Merith's brother Mark Ernst (R) and nephew Logan Ernst (L) in front of a 50-foot snowman named “Granddaddy” in Gilman, Minnesota, March 6, 2014. (Photo by Eric Miller/Reuters)

“7584 Fish”. On a windy day right after a Cyclone passed the far northern Great Barrier Reef i took some friends out to the reef. Never before i saw that many glass fish on this particular coral “bommie”. Just when i setup my camera, this Napoleon Wrasse swam right through the school of fish building a living frame. Photo location: Cairns, Great Barrier Reef, Flynn Reef, Australia. (Photo and caption by Christian Miller/National Geographic Photo Contest)

Syrian refugees sit behind barbed wire as they wait to cross into Macedonia at the Greek-Macedonian border, near the village of Idomeni, August 21, 2015. (Photo by Yannis Behrakis/Reuters)

Model Alessandra Ambrosio (L) and Adriana Lima walk the runway during the 2011 Victoria's Secret Fashion Show at the Lexington Avenue Armory on November 9, 2011 in New York City. (Photo by Jamie McCarthy/Getty Images)

People attend a Halloween event at Ocean Park on October 30, 2015 in Hong Kong. Halloween – a named taken from 'All Hallows' Even' falls on the day before All Saints' Day on November 1 – a holiday when Christians remember their deceased loved ones. (Photo by Anthony Kwan/Getty Images)

A young man looks over his shoulder as men watching a soccer match in a nearby bar ask why he isn't watching the game, while walking with his date during the men's gold medal soccer match between Brazil and Germany during Rio 2016 on Saturday, August 20, 2016. (Photo by Aaron Ontiveroz/The Denver Post)