In this Wednesday, July 13, 2016, handout image provided by Solar Impulse, the Solar Impulse 2 flying over the pyramids, Egypt Cairo. The experimental solar-powered airplane has arrived in Egypt as part of its global voyage. (Photo by Jean Revillard, Rezo via the AP Photo)

A Dancer, dressed with the traditional Yi costume, waits to perform at the Torch Festival, in Xichang, China's Sichuan province on July 27, 2016. As a result of fast urbanisation in the rural area of China Like Lienchang prefecture, the traditional costume is fading away for the Yi people in daily life. (Photo by Fred Dufour/AFP Photo)

Inmates sleep on the steps of a ladder inside the Quezon City jail at night in Manila in this picture taken on July 21, 2016. There are 3,800 inmates at the jail, which was built six decades ago to house 800, and they engage in a relentless contest for space. Men take turns to sleep on the cracked cement floor of an open-air basketball court, the steps of staircases, underneath beds and hammocks made out of old blankets. (Photo by Noel Celis/AFP Photo)

Two boys look out from the Mangueira slum towards the Maracana Stadium that is hosting the Rio's 2016 Summer Olympics opening ceremonies, in Rio de Janeiro, Brazil, Friday, August 5, 2016. (Photo by Leo Correa/AP Photo)

An Afghan girl makes a pile of unbaked bricks near the road passing through the Shamali Plains, about 10 kilometers (6 miles), west of Bagram, Afghanistan, Wednesay April 9, 2003. Children assist parents in their job to supplement family income. (Photo by Gurinder Osan/AP Photo)

In this picture taken Friday, September 8, 2017, Brazilan Samba dancers perform on stage during the Harare International Carnival in the capital. An international carnival aimed at boosting the local tourism industry has ended in economically troubled Zimbabwe. Some viewed the Harare festivities, which ended Sunday and featured artists and dancers from Brazil, Cuba, Egypt and elsewhere, as a relief from the struggle to get by in the southern African country. (Photo by Tsvangirayi Mukwazhi/AP Photo)

In 2013, the United Nations General Assembly officially designated November 19 as World Toilet Day, which is coordinated by UN-Water in collaboration with governments and partners. Here: An open-air toilet and a hot spring shower are seen in the middle of nowhere on the road to the Krafla geothermal power station and lava fields, near Reykjahlid and Lake Myvatn in northeastern Iceland, on August 19, 2012. (Photo by Mariana Suarez/AFP Photo)

A tattoo of a weapon covers the arm of a female inmate waiting to compete in the annual beauty contest at Talavera Bruce penitentiary in Rio de Janeiro, Brazil, early Thursday, November 23, 2017. Jail authorities say they organize the annual contest to encourage self-esteem, fight idleness and promote integration among women prisoners. (Photo by Silvia Izquierdo/AP Photo)