Mamoni Mandal, member of the Rapid Action Force (RAF), attends a training session at a police training school in Kolkata April 15, 2007. (Photo by Parth Sanyal/Reuters)

The new 2011 Volkswagen Passant Variant (L) and new Golf Cabrio are lifted into one of two storage towers at the Autostadt customer reception center at the Volkswagen factory on the day of the German automaker's annual press conference on March 10, 2011 in Wolfsburg, Germany. (Photo by Sean Gallup/Getty Images)

The 3D street painting “Crevasse” by artist Edgar Mueller is seen in this undated picture during the “Festival of culture”, 2008 in Dun Laoghaire, Irland. Edgar Mueller put a part of the eastern Pier into the ice age. This project has been supported by the Goethe Institution Germany. (Photo by Edgar Mueller/Getty Images)

Two men standing on a high catwalk, surveying the construction of the Brooklyn Bridge, with Manhattan in the background, New York City, 1877. (Photo by Museum of the City of New York/Archive Photos/Getty Images)

Growing cities, overuse of fertilizers and factory wastewater have degraded China's water supplies to the extent that half the nation's rivers and lakes are severely polluted. China aims to spend $850 billion to improve filthy water supplies over the next decade, but even such huge outlays may do little to reverse damage caused by decades of pollution and overuse in Beijing's push for rapid economic growth. Photo: Fishermen row a boat in the algae-filled Chaohu Lake in Hefei, Anhui province, June 19, 2009. (Photo by Jianan Yu/Reuters)

A British soldier from 3 Commando Brigade looks through the sight of his sniper rifle at Camp Gibraltar February 24, 2003 near Kuwait City, Kuwait. (Photo by Ian Waldie/Getty Images)

The Mayon volcano continues to erupt as the sun sets behind Legazpi city, Thursday, January 25, 2018 in Albay province, roughly 340 kilometers, (200 miles) southeast of Manila, Philippines. (Photo by Bullit Marquez/AP Photo)