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: Anaesthesia
[{'content': 'Which anaesthetic gas has high propensity to accumulate in cavities? \nSelect and explain. \nA. Halothane, B. Nitrous oxide, C. Ether, D. Sevoflurane', 'role': 'user'}, {'content': 'Answer: B \nExplanation: N2O can increase pressure significantly in closed air spaces (cavities) because for 1 mole of nitrogen removed 35 moles of N2O is replaced.', 'role': 'assistant'}]