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A worker walks through the TransCanada Corp. Houston Lateral Project pipe yard in Mont Belvieu, Texas, U.S., on Wednesday, March 5, 2014. Russ Girling, TransCanada Corp. president and chief executive officer, said he remains 'optimistic' that market forces will see that the embattled Keystone XL oil sands pipeline is built, but the real question is when. Photographer: Scott Dalton/Bloomberg via Getty Images

A worker walks through the TransCanada Corp. Houston Lateral Project pipe yard in Mont Belvieu, Texas, U.S., on Wednesday, March 5, 2014. Russ Girling, TransCanada Corp. president and chief executive officer, said he remains 'optimistic' that market forces will see that the embattled Keystone XL oil sands pipeline is built, but the real question is when. Photographer: Scott Dalton/Bloomberg via Getty Images