Acetylene, Achievement awards, Acts of God, Affidavits, Age 55 or over, Age 65 or over, Agricultural irrigation projects, Agricultural labor, Aircraft, Air force, Alaska, Alcohol fuel credit, Aliens, Alimony and separate maintenance payments, Alternative minimum tax, Ambulances, Ammonia, Amortization, Amusement expenses, Anti-cruelty organizations, Apostolic associations, Apothecaries, Aquatic resources trust fund, Arbitrage bonds,… —Research Institute of America Index to Internal Revenue Code