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 organism causing pseudomembranous colitis: \nSelect and explain. \nA. Clostridium difficile, B. Clostridium perfringens, C. Clostridium tetani, D. Clostridium botulinum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Clostridium difficile', 'role': 'assistant'}]