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 procedure (in Class III restoration) shown is: \nSelect and explain. \nA. Smoothening of enamel margin, B. Beveling of the external tooth surface, C. Refining the proximal walls, D. Flaring of proximal walls', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Larger preparations may require additional beveling of the accessible enamel walls to enhance retention by bonding these enamel margins, which are beveled with a flame-shaped or round diamond instrument.\nThe bevel is prepared by creating a 45-degree angle to the external surface and to a width of 0.5 to 2 mm, depending on the size of the preparation, location of the margin, and esthetic requirements of the restoration.', 'role': 'assistant'}]