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
In comparison to the apex of the lung, the base of the lung has 
Select and explain. 
A. High pulmonary arterial pressure O2, B. High pulmonary arterial pressure CO2, C. High ventilation / perfusion ratio, D. Same ventilation / perfusion ratio
B: High pulmonary arterial pressure CO2
Answer: B: High pulmonary arterial pressure CO2 
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.