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': 'Over denture used to \nSelect and explain. \nA. Preserve alveolar bone, B. Maintain proprioception from periodontal ligament, C. Retention, D. All of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]