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
Which of the following drugs does not affect absorption and secretion of cerebrospinal fluid? 
Select and explain. 
A. Halothane, B. Nitrous oxide, C. Ketamine, D. Thiopentone sodium
B: Nitrous oxide
Answer: B: Nitrous oxide 
Explanation: Ans. b. Nitrous oxide