There was no let-up in the flight from stocks and bonds Thursday; the Dow’s plunge wiped out nearly two months’ gains. On Wednesday, the Fed roiled markets when it said it could start rolling back its stimulus this year and end it next year. China’s manufacturing slowdown added to the worries. The Dow’s drop was its biggest since 2011 and came just three weeks after the blue-chip index hit a record high of 15,409. The S&P 500 also set a record last month. Smallcompany stocks fell more than others, a sign investors are aggressively cutting risk. In government debt, the yield on the 10-year note rose to its highest since August 2011.