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': 'In the etiology of dental caries, one of the following is\nnot an environmental factor \nSelect and explain. \nA. Saliva, B. Micro organisms, C. Refined carbohydrates, D. Structure of the tooth', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]