This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inhalational Anesthetic Agents, Subject name: Anaesthesia
Minimal mandatory Percentage of oxygen used in general anaesthesia is 
Select and explain. 
A. 33%, B. 30%, C. 21%, D. 66%
B: 30%
Answer: B: 30% 
Explanation: minimum mandatory is 30% oxygen. Less than 30 % can only is allowed in surgeries with high risk of fire hazard. There we decrease oxygen under strict monitoring.