WASHINGTON, Nov. 23 (Xinhua) -- U.S. President Barack Obama's administrator in Medicare agency, a key player in carrying out the healthcare reform, will resign after his nomination was blocked by Senate Republicans, local media reports quoted officials as saying on Wednesday. The administrator of the Center for Medicare and Medicaid Services, Don Berwick, will leave his post on Dec. 2, and his deputy Marilyn Tavenner, will take over, according to The Hill, a newspaper specializes in covering the Congress. Berwick, a Harvard professor known for his work in improving health care system, was nominated in April, 2010, to help carry...