This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Preoperative assessment and monitoring in anaesthesia, Subject name: Anaesthesia
[{'content': 'When using low-flow circle absorber techniques, the uptake of nitrous oxide must be considered. In a healthy 70 kg adult the expected uptake of nitrous oxide, with a 70% inspired concentration, after 1.5 hours would be about \nSelect and explain. \nA. 1000 ml.min-1, B. 500 ml.min-1, C. 250 ml.min-1, D. 100 ml.min-1', 'role': 'user'}, {'content': 'Answer: D \nExplanation: uptake of N2O (in mls/min) is equal to 1000 divided by the square root of the time elapsed (in mins) * the time elapsed is 100 minutes. * the square root of this is 10 * 1000 divided by 10 is 100 so the N2O uptake at 100 mins into the case would be about 100mls/min.', 'role': 'assistant'}]