When Glucagon Binds to Its Receptor on a Liver Cell

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