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
Cyclic AMP increase the rate of glycogenolysis by 
Select and explain. 
A. 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
A: Promoting the formation of phosphorylase
Answer: A: Promoting the formation of phosphorylase 
Explanation: 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