Required: Indicate whether each of the following items is considered a primary authority or a secondary authority

Required: Indicate whether each of the following items is considered a primary authority or a secondary authority. a. Reg. Sl .305-1 b. Rev. Rui. 67-225, 1967-2 C.B. 238. c. S.M. Jones, S.C. Rhoades-Catanach, and S. Callaghan, Principles of Taxation for Business and Investment Planning (New York: McGraw-Hill Education, 2017). d. PLR 201240007. e. Helvering v. Alabama Asphaltic Limestone Co., 315 U.S. 179 (1942). f. United States Tax Reporter Code Arranged Explanations 11614 Gross income defined.