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': 'Experimental gingivitis was first reported by \nSelect and explain. \nA. Carranza, B. Newman, C. Robert koch, D. Herald Loe', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]