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': 'What is the root value of the posterior cutaneous nerve of the thigh? \nSelect and explain. \nA. S1, S2, B. S1, S2, S3, C. S2, S3, D. S2, S3, S4', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Posterior cutaneous nerve of thigh- S1,2,3', 'role': 'assistant'}]