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: Surgery
[{'content': "Mayo's operation is done for - \nSelect and explain. \nA. Spigelian hernia, B. Femoral hernia, C. Richer's hernia, D. Umbilical hernia", 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]