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': 'Retention of inlay is increased by \nSelect and explain. \nA. Increased axial length of preparation, B. flat pulpal walls, C. Rounded internal line angles, D. all of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]