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': 'Preformed enterotoxins are formed by ? \nSelect and explain. \nA. Clostridium tetani, B. E.coli, C. Shigella sonnei, D. Clostridium perfringens', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]