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': 'Clostridia is? \nSelect and explain. \nA. Gram positive aerobe, B. Gram positive obligate anaerobe, C. Gram negative rods, D. Gram negative bacillus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Gram positive obligate anaerobe REF: Jawetz\'s microbiology 24th edition chapter 12 "The clostridia are large anaerobic, gram-positive, motile rods"', 'role': 'assistant'}]