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': "Best retainer advised after the closure of midline\ndiastema is \nSelect and explain. \nA. Hawley's retainer, B. Hawley's retainer with finger spring, C. Positioner, D. Bonded retainer", 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]