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
[{'content': 'Ratio of O2 : N2O in Entonox is – \nSelect and explain. \nA. 50:50:00, B. 60:40:00, C. 40 : 60, D. 25 : 75', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Entonox contain equal amount (50/50) of N2O and O2.', 'role': 'assistant'}]