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': 'Terminal mandibular molar anchor teeth requiring preparations involving the distal surface; retainer used is \nSelect and explain. \nA. W27, B. W56, C. W7, D. W8', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]