Most U.S. stocks are rising on Thursday, but a drop for Oracle is holding Wall Street back as investors question whether its big spending on artificial-intelligence technology will pay off.The S&P 500 fell 0.4% in early trading and pulled a bit further from its all-time high, which was set in October. The Dow Jones Industrial Average was up 233 points, or 0.5%, as of 9:35 a.m. Eastern time, and the Nasdaq composite was 0.7% lower.Oracle was one of the heaviest weights on the market and sank 14.5% even thoug ...