Last week's ugly sell-off continued into Monday morning as markets plunged moments after the open. The Dow Jones industrial average fell 257.26 points, to 25,258.63, while the broader S&P 500 shed 21.28 points, to 2,740.85, and the Nasdaq slipped 60.24 points, to 7,180.71. Monday's action comes after now-former Federal Reserve Chair Janet Yellen appeared on...