Cars pack a Kurdish checkpoint as residents flee Mosul in northern Iraq. The city was overrun by Islamic militants last week. Dan Kitwood/Getty Images hide caption

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A monument to Ukrainian writer Taras Shevchenko is silhouetted against a sign advertising Russia's natural gas giant Gazprom in Moscow. Gazprom has dramatically increased the price it charges Ukraine in recent months. Alexander Zemlianichenko/AP hide caption

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Shoppers gaze at a jewelry store display window in the Turkish capital Ankara on Feb. 19. Some economists have coined the term MINT to include the up-and-coming emerging markets of Mexico, Indonesia, Nigeria and Turkey. But Turkey has been hit by street protests, and others in the group have had their share of recent turbulence. Adem Altan/AFP/Getty Images hide caption

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Gas and oil extraction using hydraulic fracturing, or fracking, is at the heart of the recent U.S. oil and gas boom. Here, an oil field on the Monterey Shale formation in McKittrick, Calif. David McNew/Getty Images hide caption

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