U.S. stocks fell sharply Thursday. The Dow Jones industrial average fell 559.85, or 1.75 percent, to 31,402.01. The broader Standard & Poor's 500 index fell 96.09, or 2.45 percent, to 3,829.34. The technology-heavy Nasdaq composite index fell 478.54, or 3.5 percent, to 13,119.43.