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': 'Most common site for Ca. Large bowel  is \nSelect and explain. \nA. Sigmoid, B. Rectum, C. Ascending colon, D. Descending colon', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Rectum is most common location. (if option is not given then retco - sigmoid region).', 'role': 'assistant'}]