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': 'Early invading bacteria in carious lesions are called \nSelect and explain. \nA. Microcosm, B. Pioneer bacteria, C. Advancing bacteria, D. Anaerobic bacteria', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]