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 most frequent non-sporing anaerobic bacilli isolated from clinical specimens is \nSelect and explain. \nA. Bacteroides fragilis, B. Clostridium tetani, C. Prevotella melaninogenica, D. Fusobacterium nucleatum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]