U.S. stocks rallied on Thursday, moving the S&P 500 back in positive territory for 2011 ahead of the last trading day of the year, on more positive signals on the U.S. economy. The S&P 500 edged above its 200-day moving average, a key measure of the market's long-term momentum, but scant volume increased volatility, and made the gains harder to trust. Europe's sovereign debt crisis has been the primary concern for U.S. investors in 2011. Mixed results on an auction of long-term Italian bonds was another sign bond markets remain worried about the euro zone. With trading thin, the only bit of suspense left for U.S. ... (full story)