A P-51 Mustang named “Charlotte's Chariot” from the Southern Heritage Air Foundation flies past a cloud of smoke and fire from a nearby battle reenactment during the Wings Over Houston Airshow in Houston, on Saturday, November 1, 2014. Battle reenactments are part of the yearly show held at Ellington Airport. (Photo by Kar Hlava/AP Photo/Bay Area Citizen)

Pakistani students look out from a vehicle on their way to school near the Army Public School which was targeted by Taliban militants last year, in Peshawar, Pakistan, Monday, January 12, 2015. (Photo by B.K. Bangash/AP Photo)

Actor Bella Thorne (L) and model Amber Rose at the NYLON Young Hollywood Party at AVENUE Los Angeles on May 2, 2017 in Los Angeles, California. (Photo by Joe Scarnici/Getty Images for NYLON)

Max Gold, 20, of NYC, cruises on his skateboard as thousands gather on the National Mall for the March for Science on Saturday, April 22, 2017, in Washington, DC. Activists and scientists descend on the nation's capital to rally for environmental causes and government policies rooted in scientific research as part of the Earth Day and March for Science rallies. (Photo by Jahi Chikwendiu/The Washington Post)

This photo provided by Netflix/naturepl.com and WWF-International shows an African Elephant (Loxodonta africana) in front of double rainbow, in Masai Mara, Kenya, included in the Netflix natural history series, “Our Planet”, in collaboration with Silverback Films and WWF. The eight-part series debuts in 2019. (Photo by Andy Rouse/Naturepl/WWF-International/Netflix via AP Photo)

Engine driver Josef Kowatsch (top L) steers a train through the NEAT Gotthard Base Tunnel during a media visit near the town of Erstfeld August 24, 2015. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016, consisting of two parallel single track tunnels, each of a length of 57 km (35 miles). (Photo by Arnd Wiegmann/Reuters)

In this March 2, 2018 photo, an Andean man rests with his llama while tourists take in the natural wonder of Rainbow Mountain in Pitumarca, Peru. Tourists gasp for breath as they climb for two hours to the 16,404-foot (5,000-meter) peak in the Peruvian Andes, but stunned by the magical beauty that unfurls before them. (Photo by Martin Mejia/AP Photo)

A waste picker unloads garbage at a waste transfer station in Bamako, Mali, August 19, 2018. In the Malian capital of Bamako, donkey carts driven by young men like 19-year-old Arouna Diabate play a vital role battling the fast-growing city's waste problem. Every morning before dawn, Diabate hitches his donkey to a cart and sets off on his rounds, going door-to-door to collect household garbage which he delivers to a local waste transfer station for a monthly salary of around $35. “I won't be picking up trash with a donkey cart for the rest of my life, but for now people appreciate us because we help clean up the homes of Bamako”, Diabate said. (Photo by Luc Gnago/Reuters)