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
Phosphorylase b is maintained in an inactivated state by 
Select and explain. 
A. ATP, B. cAMP, C. Calcium, D. Insulin
D: Insulin
Answer: D: Insulin 
Explanation: Question is repeasted