This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
[{'content': "Cyclic AMP increase the rate of glycogenolysis by \nSelect and explain. \nA. Promoting the formation of phosphorylase, B. Acting as a cofactor for glycogen phosphorylase, C. Furnishing phosphate for the phosphorylysis of glycogen, D. Acting as a precursor of 5' AMP which is a cofactor for glycogen phosphorylase", 'role': 'user'}, {'content': 'Answer: A \nExplanation: The roles of cAMP and inorganic phosphate (Pi) in the regulation of muscle glycogenolysis during exercise have been investigated in humans using the needle biopsy technique. The fraction of phosphorylase a in resting muscle was as a mean 23%, but the rate of glycogenolysis was extremely low. Epinephrine infusion increased cAMP in muscle by 3-fold and transformed 80% of phosphorylase to the form', 'role': 'assistant'}]