US STOCKS-S&P 500, Nasdaq dip on Yellen's comments; Apple up late By: Reuters: Company News July 15, 2014 at 17:55 PM EDT * Yellen, Fed policymakers: Some U.S. stock valuations 'stretched' Read More >> Related Stocks: Apple Blackberry Ltd Facebook GX Social Media ETF Goldman Sachs Group International Business Machines JPMorgan Chase & Co Johnson & Johnson Yahoo