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': 'Smaller straight elevator work on: \nSelect and explain. \nA. Wedge principle., B. Lever principle., C. Both, D. Any of the above.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]