With the prospect of stiffer sanctions against Russia rattling confidence in Europe, investors will be looking to the United States and China to underpin the global economy. Wednesday’s U.S. gross domestic product (GDP) reading and jobs data on Friday will help markets to judge the strength of the economy’s rebound and the likely speed of the Federal Reserve’s return to more conventional monetary policy. The Fed meets on Tuesday and Wednesday. “The U.S.-China story is looking more encouraging,” said James Knightley, an economist with ING.