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
What is seen in CO poisoning? 
Select and explain. 
A. Oxygen curve shifts to left, B. Hypoxic hypoxia, C. Cyanosis, D. Diffusion capacity of lung decreases
A: Oxygen curve shifts to left
Answer: A: Oxygen curve shifts to left 
Explanation: None