32. Which of the following correctly describes the second messenger pathway activated by epinephrine binding to a β-adrenergic receptor? (PDE = phosphodiesterase; cAMP = cyclic adenosine monophosphate; PKA = protein kinase A; AC = adenylyl cyclase) (A) PDE activation → cAMP formation → PKA activation → protein phosphorylation (B) PDE activation → cAMP formation → protein phosphorylation → PKA activation (C) AC activation → cAMP formation → protein phosphorylation → PKA activation (D) AC activation → cAMP formation → PKA activation → protein phosphorylation