Men cover their heads from the sun while riding on a motorcycle during a hot day in Cairo, Egypt, August 17, 2015. A heatwave killed at least 61 people across Egypt from Sunday to Tuesday and caused nearly 600 people to be admitted to hospital, Egypt's health ministry said on state news agency MENA on Wednesday. (Photo by Amr Abdallah Dalsh/Reuters)

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)

A Palestinian protester sets fire to himself as he throws a molotov cocktail during clashes with the members of the Israeli armed forces in the West Bank city of Hebron, 13 October 2015. The past 12 days have seen the worst spell of street violence in Israel and the Palestinian areas in years, stirred in part by Muslim anger over perceived changes to the status quo observed at a disputed Jerusalem holy site. Sixteen Palestinians from the West Bank and Jerusalem have been killed, but more than half of them have been attackers shot dead after or during attempts to stab Israelis. (Photo by Abed Al Hashlamoun/EPA)

A small section of the expanding remains of the Veil Nebula, a massive star that exploded about 8,000 years ago. The entire nebula is 110 light-years across, covering six full moons on the sky as seen from Earth, and resides about 2,100 light-years away in the constellation Cygnus, the Swan. Image taken by NASA's Hubble Space Telescope. Released September 24, 2015. (Photo by Reuters/NASA/ESA/Hubble Heritage Team)

In this Tuesday, December 15, 2015 photo, an Afghan man sells traditional sauces and pickles on a street in Kabul, Afghanistan. (Photo by Massoud Hossaini/AP Photo)

In this November 21, 2015 photo, Camila Lopez Rivas, 14, poses for portraits on a beach in Havana, Cuba, as an assistant lifts the train of her dress to make it look like its flying in the wind. Camila lives in Miami, the daughter of a truck driver who left Cuba when she was a baby. She doesn't remember the island, but wanted to return for the photographs and videos that Latin American girls typically take for their 15th birthdays. (Photo by Ramon Espinosa/AP Photo)

A spectator at the Maslenitsa car battle, reacts during a clash, in the village of Goroshki, some 35 kilometers from Minsk, Belarus, 12 March 2016. The battle which is held at the Historical and Cultural Complex, Stalin line, is a small local competition, with participants from Belarus and Russia. (Photo by Tatyana Zenkovich/EPA)

Characters dressed as Elmo and Cookie Monster who pose for tips take a photo by request from a tourist (2nd R, black pants) in Times Square in the Manhattan borough of New York City, January 29, 2016. (Photo by Rickey Rogers/Reuters)