Andrey Karr from Western Riders Slacklines at sunset above big waves in Nazare, Portugal on December 27, 2017. (Photo by Aidan Williams/National Geographic Travel Photographer of the Year Contest)

In this Thursday, February 9, 2017 photo, a Bangladeshi boy pulls a rickshaw loaded with strips of leather at the highly polluted Hazaribagh tannery area in Dhaka, Bangladesh. Hazardous, heavily polluting tanneries with workers as young as 14 supplied leather to companies that make shoes and handbags for Western brands, a nonprofit group that investigates supply chains says. (Photo by A.M. Ahad/AP Photo)

Dancers at the Windmill Theatre in London, England practice a routine wearing gas masks and hard-hats with their costumes, 1940. (Photo by Hulton Archive/Getty Images)

A woman walks with a squirrel on her shoulder at Maeklong market at the outskirts of Bangkok, Thailand September 20, 2016. (Photo by Jorge Silva/Reuters)

Two stallions confront each other at a horse fighting contest in Rongshui, China. More than 30 horses from surrounding regions took part in the traditional activity of the Lantern festival. (Photo by China Foto Press)

This Thursday, April 30, 2015 photo shows Lebanese citizens walking on the Corniche, or waterfront promenade in Beirut, Lebanon. This photo was shot through the lowered veil of a niqab, which is worn by some conservative Muslim women. The cloth allows women to follow a strict interpretation of their religious beliefs by preventing others from seeing their faces. (Photo by Hassan Ammar/AP Photo)

Evan Leversage, who is terminally ill with brain cancer, is greeted by a Christmas decorated dog with his mother Nicole Wellwood (L), and his father Travis Leversage (2nd R) in St. George, Ontario, Canada October 24, 2015. Evan Leversage is a seven-year-old boy who has been living with inoperable brain cancer since he was two years old. His family has organized a Christmas celebration in October complete with a full parade, in case Evan does not live to celebrate his last Christmas day on the traditional date of December 25, according to local media. (Photo by Mark Blinch/Reuters)

Aisha, 15, (L) (who asked to withhold her last name), a Syrian refugee from Raqqa, waits with a fellow refugee while harvesting cannabis in the Bekaa valley, Lebanon October 19, 2015. Syrian refugees work to harvest and process spiky-leafed cannabis plants in neighbouring Lebanon’s Bekaa Valley. Often farmers of cotton and wheat back home in Raqqa province – now the de facto capital of Islamic State – the conflict in Syria drove them to seek safety in a region where Syrian migrant workers used to spend a few months a year before returning home. (Photo by Alia Haju/Reuters)