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
A decrease in the arterial PO2 is seen in: 
Select and explain. 
A. Decrease in hemoglobin concentration of arterial blood, B. Paralysis of inspiratory muscles, C. Sluggish blood flow, D. High altitudes
D: High altitudes
Answer: D: High altitudes 
Explanation: None