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': 'Which of the following is the commonest site for Ca colon? \nSelect and explain. \nA. Caecum, B. Sigmoid colon, C. Ascending colon, D. Transverse colon', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The frequency is sigmoid colon > caecum > transverse colon > ascending colon.', 'role': 'assistant'}]