This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
[{'content': 'Acute emphysematous cholecystitis is caused by - rpt \nSelect and explain. \nA. Pseudomonas aeruginosa, B. Staph. Aureus, C. Clostridium perfringes, D. Strep. Pyocynacae', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Question repeated.', 'role': 'assistant'}]