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
[{'content': "Which enzyme is deficient in Mc Ardle's disease? \nSelect and explain. \nA. Liver phosphorylase deficiency, B. Muscle phosphorylase deficiency, C. Lysosomal alpha-1, 4 glucosidase deficiency, D. G6PD deficiency", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Repeated question', 'role': 'assistant'}]