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
Which enzyme is deficient in Mc Ardle's disease? 
Select and explain. 
A. Liver phosphorylase deficiency, B. Muscle phosphorylase deficiency, C. Lysosomal alpha-1, 4 glucosidase deficiency, D. G6PD deficiency
B: Muscle phosphorylase deficiency
Answer: B: Muscle phosphorylase deficiency 
Explanation: Repeated question