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 which O2 therapy is used ? 
Select and explain. 
A. Hypoxic hypoxia, B. Anemic hypoxia, C. Histotoxic, D. Stagnant
A: Hypoxic hypoxia
Answer: A: Hypoxic hypoxia 
Explanation: Ans. is 'a' i.e., Hypoxic hypoxia