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: Dental
[{'content': 'The lever action that occurs in distal extension partial dentures is \nSelect and explain. \nA. 1st - order Lever, B. 2nd - order lever, C. 3rd - order lever, D. 4th - order lever', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]