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: Medicine
[{'content': 'The most common cause of painless bleeding P.R. in a man is - \nSelect and explain. \nA. Fissure-in-ano, B. Diverticulosis, C. Piles, D. None', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]