This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Musculoskeletal  disorders, Subject name: Pediatrics
[{'content': 'EMG is least useful for diagnosis of \nSelect and explain. \nA. Cerebral palsy, B. Spinal muscular atrophy, C. Charot-Marie-Tooth disease, D. Myasthenia gravis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: EMG is leastly used in cerebral palsy since the cause is in the brain and not in the muscles', 'role': 'assistant'}]