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
Size in < 6 years old child, of endotracheal tube is 
Select and explain. 
A. Age +3.5/3.5, B. Age +2.5/2.5, C. Age + 4.5/4.5, D. Age -4.5/4.5
A: Age +3.5/3.5
Answer: A: Age +3.5/3.5 
Explanation: A i.e. Age +3.5/3.5