Wall Street lower as rate hike uncertainty returns

U.S. stocks dropped on Friday, with investors again focusing on when the Federal Reserve will hike interest rates next and with the corporate earnings season winding down. Investors were also cagey ahead of next week's annual meeting of central bankers from around the world in Jackson Hole, Wyoming, in which Fed Chair Janet Yellen is likely to cement expectations for a slow pace of rate increases. Recent hawkish comments from two Fed officials have clashed with the central bank's position that m