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: Surgery
[{'content': 'The gas used in LA cartridge \nSelect and explain. \nA. O2, B. Helium, C. N2, D. CO2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]