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': 'Material of choice for single-step border moulding is \nSelect and explain. \nA. Polyether, B. Greenstick compound., C. ZOE, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Single step or simultaneous border moulding:\nIt is a process, in\xa0which the entire periphery of the tray is refined in a single step. Polyether impression material is the material of choice because it fulfills all the requisites.', 'role': 'assistant'}]