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)

Participants dressed in historical clothing ride high-wheel bicycles during a bicycle ballet event at Schloss Karlsruhe palace during the 2017 International Veteran Cycle Association (IVCA) rally to celebrate the 200th anniversary of the bicycle on May 27, 2017 in Karlsruhe, Germany. Karl Drais, a German inventor, built and tested the first bicycle, called the Draisine, that ran without pedals in 1817. (Photo by Alexander Scheuber/Getty Images)

A Hindu devotee performs a stunt with fire during a rehearsal for the annual Rath Yatra, or chariot procession, which commemorates a journey by Hindu god Jagannath, his brother Balabhadra and sister Subhadra, in specially made chariots, in Ahmedabad, India, June 26, 2016. (Photo by Amit Dave/Reuters)

A man lays in front of a tank in the entrance to Istanbul's Ataturk airport, early Saturday, July 16, 2016. Members of Turkey's armed forces said they had taken control of the country, but Turkish officials said the coup attempt had been repelled early Saturday morning in a night of violence, according to state-run media. (Photo by Ismail Coskun/IHA via AP Photo)

Attendees dressed as Poison Ivy and Harley Quinn arrive for opening day of the annual Comic-Con International in San Diego, California, United States July 21, 2016. (Photo by Mike Blake/Reuters)

Seen in a long exposure nighttime photograph, a burned van rests in a lot while a wildfire glows on the horizon in Phelan, Calif., early Thursday, August 18, 2016 2016. (Photo by Noah Berger/AP Photo)

Indian models showcase creations by designer Shivan & Naresh during the Lakme Fashion Week (LFW) Winter/Festive 2016 in Mumbai on August 27, 2016. (Photo by Sujit Jaiswal/AFP Photo)

The US Navy Blue Angels numbers 5 and 6 fly below Sean Tucker (above) as he pilots the Oracle Challenger III over San Francisco, California as part of a practice run for Fleet Week on October 6, 2016. (Photo by Josh Edelson/AFP Photo)