This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
[{'content': 'Acute emphysematous cholecystitis is caused by \nSelect and explain. \nA. Pseudomonas aeruginosa, B. Staphylococcus, C. Clostridium perfringens, D. Streptococcus pyogenes', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Emphysematous cholecystitis It is thought to begin with acute cholecystitis (calculous or acalculous), followed by ischaemia or gangrene of GB wall and infection by gas producing organisms. Causative organisms of Emphysematous Cholecystitis Anaerobes : Clostridium welchi or Cl. Perfringens Aerobes : E.coli Ref: Sabiston 20th edition Pgno : 1493', 'role': 'assistant'}]