The handgun sales counter at Northwest Armory in Portland, Ore. David Gilkey/NPR hide caption

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Gas prices are displayed at a service station in Leonia, N.J., Nov. 24. Gas is under $2 a gallon across much of the country and the price is expected to remain low next year. Seth Wenig/AP hide caption

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Shell's Jack Pine Mine near Fort MacKay, Alberta. The largest trucks, called "heavy haulers," can hold 400 tons of oil sands material. It takes 2 tons to produce one barrel of oil. Jeff Brady/NPR hide caption

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Bill Cosby performs during a November 2014 show at the Maxwell C. King Center for the Performing Arts in Melbourne, Fla. Phelan M. Ebenhack/AP hide caption

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The Southeastern Pennsylvania Transportation Authority tests its Positive Train Control system at the agency's rail yard near Malvern, Pa. The system will cost SEPTA about $328 million. The regional passenger railroad is one of the few in the country that are on track to meet an end-of-the-year deadline for installing PTC. Jeff Brady/NPR hide caption

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