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': 'The cavosurface margin for direct filling gold are prepared with \nSelect and explain. \nA. 90° butt joint, B. 45° Bevelled, C. 30-40° bevel, D. 10° bevel', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]