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
Most impoant stimulus to peripheral chemoreceptors 
Select and explain. 
A. PO2, B. CO2, C. pH, D. HCO3
A: PO2
Answer: A: PO2 
Explanation: Peripheral chemoreceptors are activated by changes in the paial pressure of oxygen and trigger respiratory drive changes aimed at maintaining normal paial pressure levels.Ref: Ganong review of medical physiology 23rd edition Page no: 562