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
Least A-V O2 difference is seen in ? 
Select and explain. 
A. Hypoxic hypoxia, B. Anemic hypoxia, C. Stagnant hypoxia, D. Cyanide poisoning
D: Cyanide poisoning
Answer: D: Cyanide poisoning 
Explanation: Ans. is 'd' i.e., Cyanide poisoning