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Fracking crews member watches over water tanks at an Anadarko Petroleum Corporation site near Brighton, May 19, 2014. (RJ Sangosti/The Denver Post via Getty Images)

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Sen. Bob Corker, R-Tenn., and Sen. Bob Menendez, D-N.J., Jan. 29, 2015. (Bill Clark/CQ Roll Call)

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U.S. Marine Corps pilots from Marine Light Attack Helicopter Training Squadron 303, Marine Aircraft Group 39, 3rd Marine Aircraft Wing maneuver a AH-1Z Viper, Marine Corps Base Camp Pendleton, California (USA), December 19, 2008. (Wikimedia)

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(TERADAT SANTIVIVUT/Getty Images)

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A Chinese man wears a mask as he waits to cross the road near the CCTV building during heavy smog on November 29, 2014 in Beijing, China. (Kevin Frayer/Getty Images)

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French Prime Minister Manuel Valls in Paris on April 29, 2015. (FRANCOIS GUILLOT/AFP/Getty Images)