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: Surgery
Nitrous oxide alone is not used as a G.A agent because of 
Select and explain. 
A. Difficulty in maintaining an adequate oxygen concentration, B. Expense of the agent and its exposure hazards, C. Adverse effect on liver, D. Poor analgesic property
A: Difficulty in maintaining an adequate oxygen concentration
Answer: A: Difficulty in maintaining an adequate oxygen concentration 
Explanation: None