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': 'Retainer less matrix that can be used for all teeth (Retainer less matrix) \nSelect and explain. \nA. Tofflemeir, B. Ivory No.1, C. Universal, D. Automatrix', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]