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
Endotracheal tube level is – 
Select and explain. 
A. 5 cms above xiphisternum, B. 4 cms above carnia, C. 1 cm above carnia, D. At carnia
B: 4 cms above carnia
Answer: B: 4 cms above carnia 
Explanation: "Ideally, the tube tip should be 5 ±2 cm from the carina when the head and neck are in neutral position".
___ Fundamental of anaesthesia

Neck flexion causes a 2 cm descent of endotracheal tube towards carina, and neck extension causes a 2cm ascent of trachial tube tip from the carina. Therefore correct position of tip of the tube is :-

5 ±2 cm from carina → When neck is neutral
3 ±2 cm from carina → When neck is flexed
7 ±2 cm from carina → When neck is extended