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: Anatomy
[{'content': 'External anal sphincter is innervated by: \nSelect and explain. \nA. S2, S3, S4, B. S2, S3, C. L5, S1, D. L2, L3', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a. S2, S3, S4', 'role': 'assistant'}]