3. When glucagon binds to its receptor on a liver cell, which of the following sequence of events occurs to activate protein kinase A? (A) activation of adenylate cyclase, activation of G protein, production of cAMP (B) activation of G protein, activation of adenylate cyclase, production of cAMP (C) activation of G protein, production of cAMP, activation of adenylate cyclase (D) production of cAMP, activation of adenylate cyclase, activation of G protein (E) none of the above