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': 'Most common organism responsible for gas gangrene \nSelect and explain. \nA. Clostridium perfringens, B. Clostridium difficile, C. Clostridium tetani, D. Clostridium septicum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]