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': 'Articulators are classified into arbitrary positional and\nfunctional by \nSelect and explain. \nA. Beak, B. Posell, C. Boucher, D. Thomas', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]