20. Starting with benzene, the best method for preparing para-nitrobenzoic acid is:
(A) HNO₃/H₂SO₄; then CH₃Cl/AlCl₃; then separation of isomers; then KMnO₄/⁻OH/heat, followed by H₃O⁺.
(B) CH₃Cl/AlCl₃; then HNO₃/H₂SO₄; then separation of isomers; then KMnO₄/⁻OH/heat, followed by H₃O⁺.
(C) CH₃Cl/AlCl₃; then KMnO₄/⁻OH/heat, followed by H₃O⁺; then HNO₃/H₂SO₄.
(D) HNO₃/H₂SO₄; then KMnO₄/⁻OH/heat, followed by H₃O⁺; then CH₃Cl/AlCl₃.
(E) HNO₃/H₂SO₄; then CO₂, followed by H₃O⁺.