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: Physiology
True statement regarding pulmonary ventilation is - 
Select and explain. 
A. PaO2 is maximum at the apex, B. V/Q is maximum at the base, C. Ventilation per unit lung volume is maximum at the apex, D. Blood circulation is minimum at the base
A: PaO2 is maximum at the apex
Answer: A: PaO2 is maximum at the apex 
Explanation: Apical alveoli have low ventilation and perfusion per unit volume of the lung, whereas the basal alveoli have high ventilation and perfusion.
Ventilation-perfusion ratio and the PaO2 is maximum at the apex. PCO2 is maximum at the base.