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: Medicine
CO poisoning is characterized by -a) Lt. shift of O2 dissociation curveb) ↓ PaCO2c) ↓ P50d) ↓ O2 Contente) Smoking is a predisposing factor 
Select and explain. 
A. acd, B. bde, C. abd, D. ade
B: bde
Answer: B: bde 
Explanation: None