The United States Federal Reserve kept key US interest rates unchanged on Wednesday, opting for a steady course as the world’s top economy expands — even in the face of financial turmoil abroad. The widely expected decision left the Fed’s rate for overnight loans between banks at 4,75%, where it has been since November. United States financial markets showed little reaction to the news. US stocks held on to earlier gains while inflation-sensitive bond prices inched lower as investors pondered when and what the central bank’s next monetary policy move will be.