As a third alternative, in those areas where Congress has not completely displaced state regulation, federal law may nonetheless pre-empt state law to the extent it actually conflicts with federal law. Such a conflict occurs either because "compliance with both federal and state regulations is a physical impossibility," "Florida Lime & Avocado Growers, Inc. v. Paul", 373 U.S. 132, 142-143, 83 S.Ct. 1210, 1217, 10 L.Ed.2d 248 (1963), or because the state law stands "as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress." "Hines v. Davidowitz", 312 U.S. 52, 67, 61 S.Ct. 399, 404, 85 L.Ed. 581 (1941)...