Stocks pulled back from the worst of Monday's losses but still ended the session in the red. A slump in crude prices put pressure on the energy sector. Fitbit (FIT) climbed after its fitness tracking app held the top spot in its category in Apple's (AAPL) App Store this holiday season. The app ranked second overall on the free apps charts. Fitbit's domination of the charts suggests promising sales of its wearable devices this holiday season. McDonald's (MCD) is testing mac and cheese on its menu. The chain has quietly rolled out the offering at a limited number of stores in Cleveland since the summer. And, 3D Systems (DDD) fell after announcing it will discontinue sales of its entry-level 3D printer. TheStreet's Keris Lahiff has details from Wall Street.