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': 'Fins in casting are seen \nSelect and explain. \nA. Round margin in casting, B. Too Long heating, C. Air bubbles on wax, D. Cracking of investment', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]