This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Energy in muscles is stored as: 
Select and explain. 
A. ATP, B. ADP, C. Phosphorylcreatine, D. None of the above
C: Phosphorylcreatine
Answer: C: Phosphorylcreatine 
Explanation: ATP is resynthesized from ADP by the addition of a phosphate group. Some of the energy for this endothermic reaction is supplied by the breakdown of glucose to CO2 and H2O, but there also exists in muscle another energy-rich phosphate compound that can supply this energy for sho periods. This compound is phosphorylcreatine, which is hydrolyzed to creatine and phosphate groups with the release of considerable energy. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 5.