Stocks sank in the pre-market after global trade balance data showed diverging trends for major economies. The US trade deficit narrowed by more than expected in December 2012. The world's biggest economy imported $38.5 billion more than it exported.  Economists expected a drop to $46 billion from $48.7 billion in November as overseas demand drove exports. Index futures this morning were mixed after yesterday's declines. Dow (INDEXDJX:.DJI) futures are down 0.05% at 13 891. Futures on the S&P 500 (INDEXSP:.INX) fell 0.01% to 1 505.20 and Nasdaq (INDEXNASDAQ:.IXIC) futures rose 0.14% to 2 745.75. Another report from the government ...