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': 'Dermatomal supply of the perianal skin is - \nSelect and explain. \nA. S1, B. L2, C. L3, D. S4', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Dermatomal supply of perianal skin and groin is S4.', 'role': 'assistant'}]