This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Peritoneum, Subject name: Surgery
[{'content': 'Most common gas used for pneumoperitoneum - \nSelect and explain. \nA. Nitrogen, B. CO2, C. O2, D. Air', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., CO2 * First Pneumoperitoneum was created by filtered room air. Carbon dioxide & N20 are now preferred gas because of increased risk of air embolism with room air.", 'role': 'assistant'}]