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': 'Size in < 6 years old child, of endotracheal tube is \nSelect and explain. \nA. Age +3.5/3.5, B. Age +2.5/2.5, C. Age + 4.5/4.5, D. Age -4.5/4.5', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Age +3.5/3.5', 'role': 'assistant'}]