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: Pharmacology
A patient, without prior medication, breathes a gas mixture consisting of 50 percent nitrous oxide and 50 percent oxygen by volume. Which of the following effects would be expected 
Select and explain. 
A. Analgesia, B. Excitation, C. Surgical anesthesia, D. Respiratory arrest
A: Analgesia
Answer: A: Analgesia 
Explanation: None