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': 'Patient presenting with abdominal pain, diarrhea taking clindamycin for 5 days. Treated with metronidazole symptoms subsided. What is the causative agent - \nSelect and explain. \nA. Clostridium difficile, B. Clostridium perfringens, C. Clostridium welchi, D. Clostridium marneffi', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Clostridium difficile", 'role': 'assistant'}]