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)

In this April 1, 2002, file photo, Mike Cole, of Jenkintown, Pa., right, performs a kick-flip over a trash can with his skateboard as tourists pose for photos in front of artist Robert Indiana's sculpture in John F. Kennedy Plaza, also known as Love Park, in Philadelphia. Granite slabs from Philadelphia's famed Love Park, a skateboarding mecca though for a long stretch an illegal one, are being shipped in 2017 to the city of Malmo, Sweden, nearly 4,000 miles away, for use in construction of a skate park there. (Photo by Douglas Bovitt/AP Photo)

A herd of elephants cross a road that passes through the flooded Kaziranga National Park in the northeastern state of Assam, India, July 12, 2017. (Photo by Anuwar Hazarika/Reuters)

As the sun sets on the Malecon in Havana on Friday January 23, 2015, Surenis Angulo de la Paz, 24, center, dances as group of locals play music around her. Behind her is Fidel Lopez, 55. (Photo by Sarah L. Voisin/The Washington Post)

Pupils of the Dao ethnic tribe return home from school along a hillside path at Suoi Thau village in Hoang Su Phi district of Vietnam's northern province of Ha Giang, located at the border with China, September 18, 2015. (Photo by Reuters/Kham)

Indian girls in traditional attire pose for photographs as they practice the Garba, the traditional dance of Gujarat state, ahead of Navratri festival in Ahmadabad, India, Saturday, October 3, 2015. Navratri or nine night festival will begin on October 13. (Photo by Ajit Solanki/AP Photo)

Master of throat singing (or Khoomei) Aikhan Orzhak (L) and model Choigana Kertek, dressed in traditional costume, perform during sunset at the Aldyn Bulak area on the bank of the Yenisei River outside the village of Ust-Elegest in Tuva region, Southern Siberia, Russia, October 7, 2015. The region is inhabited by Tuvans, historically cattle-herding nomads, who nowadays practise two main confessions – Buddhism and Shamanism. (Photo by Ilya Naymushin/Reuters)

A mahout rides on an elephant in the city of Amritsar, India, 08 November 2015. Such elephants are often accompanied by their caretakers who ask for alms from people in the streets. (Photo by Raminder Pal Singh/EPA)