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 of the following drugs does not affect absorption and secretion of cerebrospinal fluid? \nSelect and explain. \nA. Halothane, B. Nitrous oxide, C. Ketamine, D. Thiopentone sodium', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b. Nitrous oxide', 'role': 'assistant'}]