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': 'What is the purpose of Nitrogen gas filled in anaesthetic cartridge: \nSelect and explain. \nA. To maintain the pressure in the cartridge., B. To prevent deterioration of vasoconstrictor., C. To prevent deterioration of LA., D. All of the above.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The purpose of nitrogen gas-filled bubbles in the anaesthetic cartridge is to prevent deterioration of the vasoconstrictor.', 'role': 'assistant'}]