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: Microbiology
[{'content': 'The following micro - organism constitutes the normal flora of oral cavity - \nSelect and explain. \nA. Esch. coli, B. Staphylococcus epidermidis, C. Branhamella catarrhalis, D. Picornavirus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]