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
Main source of energy derived from 
Select and explain. 
A. Fat, B. Glycogen, C. Lactate, D. Ketone
B: Glycogen
Answer: B: Glycogen 
Explanation: Glycogen is the reserve carbohydrate in animals. It is stored in liver and muscles.The phosphorylated enzyme is less sensitive to allosteric inhibitors. Thus even if cellular ATP and glucose-6-phosphate are high, Phosphorylase will be active. The glucose-1-phosphate produced from glycogen in the liver may be conveed to free glucose for release to the blood.