This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
PO2 is maximum 
Select and explain. 
A. Base of lung, B. Posterior lobe, C. Apex of lung, D. Middle lobe
C: Apex of lung
Answer: C: Apex of lung 
Explanation: Paial pressure of oxygen is maximum at the apex of the lung Ref: guyton and hall textbook of medical physiology 12 edition page number: 332,333,334