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': 'Which of the following is not required for retention of cast gold restoration? \nSelect and explain. \nA. Cavosurface bevel, B. Parallel walls, C. Beveled axiopulpal line angle, D. Undermining dentinal walls', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Retention form is attained by\n\nCreating a maximum of 2-degree occlusal divergence of the vertical walls,\nAccentuating some line angles, and\nExtending the lingual surface groove to create an axial wall height in this extension of at least 2.5 mm occlusogingivally.\n\nSturdevant Operative Dentistry 7th edition page e110', 'role': 'assistant'}]