rious officers or employees of the United States by force, seel8 U.S.C. §§ III, 1501, 1502, to the obstruction of a federal law enforcement agent, seel8 U.S.C. § 3056(d), and to interference with the administration of internal revenue laws by force or threat of force, see26 U.S.C. § 7212(a). B *7 Which of these t