Afghanistan's interior ministry special forces demonstrate their skills during a military exercise in Kabul, Afghanistan, Thursday, April 2, 2015. Afghanistan's security forces took over full responsibility for the country's security on January 1, 2015. (Photo by Massoud Hossaini/AP Photo)

A boy carries empty sacks after bringing different types of plastic materials to a recycling station in Khartoum North April 16, 2015. People bring bottles and other plastic materials to the station for recycling, and get paid in return. (Photo by Mohamed Nureldin Abdallah/Reuters)

A girl looks out from the window of a “La Sabana” tourist train in La Caro March 1, 2015. The “La Sabana” tourist train that runs through the capital was founded by Eduardo Rodriguez, a railway engineer. Rodriguez has worked on Colombia's railway system his whole life and now, with an air of nostalgia, transports thousands of tourists in renovated steam locomotives that he fixes in Bogota's Central Station which dates back to 1913. (Photo by Jose Miguel Gomez/Reuters)

Pilot Akmal Bin Abdul Kahar watches South Korea's Black Eagles aerobatics team perform a manoeuvre during an aerial display at the Singapore Airshow at Changi Exhibition Center February 18, 2016. (Photo by Edgar Su/Reuters)

A Buddhist monk lights a candle at Wat Phra Dhammakaya during a ceremony on Makha Bucha Day in Pathum Thani province, north of Bangkok February 22, 2016. Makha Bucha Day honours Buddha and his teachings, and falls on the full moon day of the third lunar month. (Photo by Jorge Silva/Reuters)

A passenger takes off his pants as others not wearing pants dance while waiting for a subway train during the “No Pants Subway Ride” in Mexico City, Mexico, February 21, 2016. The event is an annual flash mob and occurs in different cities around the world, according to its organisers. (Photo by Carlos Jasso/Reuters)

Expedition 44 flight engineer and NASA astronaut Scott Kelly seen inside the Cupola, a special module which provides a 360-degree viewing of the Earth and the International Space Station. Kelly is one of two crew members spending an entire year in space. (Photo by Scott Kelly/NASA)

A member of the “Ladies in White” dissident group shouts as she is carried away by police officers after they broke up a regular march of the group, detaining about 50 people, hours before U.S. President Barack Obama arrives for a historic visit, in Havana, Cuba March 20, 2016. (Photo by Ueslei Marcelino/Reuters)