This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'Myelin sheath in CNS is produced by \nSelect and explain. \nA. Oligodendrocyte, B. Schwann cell, C. Microglia, D. Macroglia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Oligodendrocytes and Schwann cells are involved in myelin formation around axons in the CNS and peripheral nervous system respectively. Ref: Ganong&;s review of medical physiology; 23rd edition; pg: 80.', 'role': 'assistant'}]