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
In normal anaesthesia fresh minimum gas flows O2 delivery – 
Select and explain. 
A. 21%, B. 33%, C. 51%, D. 75%
B: 33%
Answer: B: 33% 
Explanation: Anaesthesia is maintained with a controlled mixture of oxygen (minimum 33%) + nitrous oxide (66%) + inhalational agent (most commonly halothane).