This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anaesthesia, Subject name: Anaesthesia
[{'content': 'Gas stored in liquid form is \nSelect and explain. \nA. Carbon dioxide, B. Nitrous oxide, C. Cyclopropane, D. Oxygen', 'role': 'user'}, {'content': 'Answer: B \nExplanation: N20 is stored in blue steel cylinders as a colorless liquid under 745 psi pressure and is in equilibrium with the gas phase (approximately 50 atmospheres at room temperature). The tank maintains that pressure until it is empty.', 'role': 'assistant'}]