Federal Reserve chief admits he is prepared to start third round of quantitative easing if US economy continues to flag Ratings agency Moody's warned it might strip the US of its AAA rating just hours after the Federal Reserve chairman, Ben Bernanke, was poised to inject further funds into the US economy and commit to several years of low interest rates to combat flagging growth and prevent further rises in the unemployment rate. Bernanke said a third round of quantitative easing, called QE3, could be necessary if the economy fails to regain momentum in the second half of the year. Moody's...