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: Pathology
[{'content': 'Bacteria responsible for initiation of caries is: \nSelect and explain. \nA. Actinomyces, B. Strep. mutans, C. Lactobacillus, D. Strep. viridans', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]