Strong gains by Apple, Facebook and other key tech stocks sent the Nasdaq exchange higher Monday while the Dow and S&P 500 sagged. The US markets were generally feeble on the first session after the slow Thanksgiving holiday week, with the jury still out over how strong the crucial Black Friday holiday sales went for retailers. At the close of trade, the Dow Jones Industrial Average was down 42.31 points (0.33 percent) at 12,967.37. The broad-market S&P 500 lost 2.86 (0.20 percent) at 1,406.29, while the Nasdaq Composite rose 9.93 (0.33 percent) to 2,976.78.