This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Bio-Chemistry), Subject name: Biochemistry
In muscle, phosphorylase b is kept in inactivated state by 
Select and explain. 
A. cAMP, B. ATP, C. Calcium, D. Glucose
A: cAMP
Answer: A: cAMP 
Explanation: (A) cAMP