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': 'A butt joint is a \nSelect and explain. \nA. 90° joint, B. 120° joint, C. 70° joint, D. 180° joint', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]