Soldiers of People's Liberation Army (PLA) Lanzhou Military Region jump through a burning obstacle during a training session at a military base in Tianshui, Gansu province, China, January 6, 2016. (Photo by Reuters/Stringer)

Children feed a giraffe at Pairi Daiza wildlife park, a zoo and botanical garden in Brugelette, Belgium, May 25, 2015. (Photo by Francois Lenoir/Reuters)

Sandra Brown, 40, rides the Skyslide on the 69th and 70th floors of the U.S. Bank Tower which is attached to the OUE Skyspace LA observation deck in downtown Los Angeles, California, U.S. June 20, 2016. (Photo by Lucy Nicholson/Reuters)

Aspiring models wait for their turn to be judged during auditions for the upcoming Lakme Fashion Week in Mumbai, India, June 30, 2016. (Photo by Shailesh Andrade/Reuters)

Paramilitary policemen take part in a training in Chaohu, Anhui province, China December 28, 2015. (Photo by Reuters/China Daily)

People take pictures of huge waves crash on the Viavelez seafront in the northern Spanish region of Asturias January 2, 2016. (Photo by Eloy Alonso/Reuters)

A girl smiles as her hair is blown by a strong wind in the Chinatown area in Yokohama, near Tokyo, Friday, January 27, 2017. (Photo by Koji Sasahara/AP Photo)

Brain-on-a-chip. Dazzling in green and magenta this image shows the nerve fibres (in green) produced by neural stem cells (in magenta) as they grow on a synthetic gel. Captured by a technique known as confocal microscopy, the image is part of research shedding light on how tinkering with the environment can affect the way in which nerve fibres grow. (Photo by Collin Edington and Iris Lee/Massachusetts Institute of Technology/Wellcome Images)