U.S. stocks retreated as the Federal Reserve signaled that financial-market turmoil may pose risks to its outlook for the U.S. economy. The dollar fell a third day versus the euro, while Treasuries held losses. The Standard & Poor’s 500 Index sank as the Fed said it is “closely monitoring” developments from China to Europe and the oil patch for any adverse impact on the U.S. economy. Apple Inc. and Boeing Co. plunged on disappointing results as the two accounted for more than half of the Dow Jones Industrial Average’s 223-point slide. The yield on 10-year Treasury notes rose toward 2 percent, as the Fed kept rates unchanged and said any future hikes would be gradual. Crude advanced past $32 a barrel. Gold gained.