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': "Nagler's reaction is shown by ? \nSelect and explain. \nA. Clostridium tetani, B. Clostridium welchii, C. Mycobacterium tuberculosis, D. Mycobacterium leprae", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]