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 frequently encountered clostridia' species in gas gangrene is \nSelect and explain. \nA. Clostridium botulinum, B. Clostridium welchii, C. Clostridium tetani, D. Clostridium difficile", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]