Wall Street opens little changed; Yellen in focus

U.S. stocks fell on Friday, weighed by a more than 4 percent drop in Oracle shares and news that a Chinese Navy warship seized a U.S. underwater drone. U.S. stocks have been on a tear since the Nov. 8 presidential election, with the S&P rising 5.7 percent on bets that President-elect Donald Trump's expected deregulation and infrastructure spending will boost the economy.