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
CO2 retention is seen in 
Select and explain. 
A. Carbon monoxide poisoning, B. Respiratory failure, C. High altitude, D. Ventilatory failure
D: Ventilatory failure
Answer: D: Ventilatory failure 
Explanation: CO2 retention seen in ventilatory failure Ref: guyton and hall textbook of medical physiology 12 edition