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)

U.S. Army soldiers with the 1st Battalion, 501st Infantry Regiment deployed to Combat Outpost Sabari, Afghanistan scan their area as they begin a multi-day air assault mission near the Pakistani border of eastern Afghanistan's Khost province May 2, 2012. (Photo by Staff Sgt. Joshua L. DeMotts/U.S. Air Force)

A full size working replica of the pink limousine used by Parker to chauffeur Lady Penelope in Gerry Anderson's television series “Thunderbirds”, unveiled at Woburn Abbey. United Kingdom, 27th May 1968. (Photo by Jim Gray/Keystone/Getty Images)

A man watches Israeli Air Force planes fly over the Mediterranean Sea from a beach at Tel Aviv during an aerial show as part of celebrations for Israel's Independence Day to mark the 66th anniversary of the creation of the state, May 6, 2014. (Photo by Nir Elias/Reuters)

Smithsonian National Zoo biologist Leigh Pitsko releases a male lion cub for its swim test in the zoo habitat moat, in Washington May 6, 2014. Four, unnamed ten-week old lion cubs were tested today for their ability to swim and remove themselves from their zoo habitat moat. (Photo by Gary Cameron/Reuters)

Israeli soldiers detain a protester during a demonstration by Palestinians protesting against the Israeli-built West Bank separation barrier and calling for the right of return for Palestinian refugees, in the northern West Bank city of Tulkarem, on May 31, 2014. (AP Photo/Nasser Ishtayeh)

A British couple drink hot chocolate at Chillout cafe in Dubai May 12, 2013. Chillout, owned by UAE's Sharaf Group, is the first ice lounge in the Middle East, with temperatures set at –6 degrees Celsius (21 degrees Farenheit). The cafe, with its illuminated interiors, curtains, paintings and seating arrangements, is all made of carved ice and frozen sculptures. (Photo by Ahmed Jadallah/Reuters)

Masked men ride in a morning procession as part of the “Cavalhadas” festival in Pirenopolis, Brazil, Sunday, May 19, 2013. The popular festival is a tradition that was introduced in the 1800's by a Portuguese priest to mark the the ascension of Christ. The 3-day festival reenacts the Christian knights' medieval defeat of the Moors. (Photo by Eraldo Peres/AP Photo)