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 caries activity test used for field study is \nSelect and explain. \nA. Lactobacillus count test, B. Streptococcus mutans, C. Snyder's test, D. Saliva /tongue blade method", 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]