U.S. economic activity continued to expand from mid-February through the end of March, but a strong dollar and falling oil prices were hurting the manufacturing sector, the Federal Reserve said on Wednesday. In its Beige Book report of anecdotal information on business activity collected from contacts nationwide, the U.S. central bank said most of its regional Fed banks described growth as either progressing at a “moderate” or “modest” pace. Weakening activity was attributed in part to the strong dollar, falling oil prices, and the harsh winter weather,” the Fed said.