Stocks gave up ground on Monday, with the Dow falling 52 points and other major market benchmarks making similar declines on a percentage basis. Many market commentators pointed to falling oil prices as one of the culprits for the downbeat day, as crude dropped below $50 per barrel to raise new concerns that the recent rebound for the energy sector could prove short-lived. Earnings-related news helped bolster some stocks, but others fell prey to downward pressure and economic uncertainty.