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': 'Mechanical advantage for straight elevator is: \nSelect and explain. \nA. 2.5, B. 3, C. 4.6, D. 2', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]