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
Which of these is not a cause of rightward shift of Oxygen – Hemoglobin dissociation curve? 
Select and explain. 
A. Increased hydrogen ions, B. Decreased CO2, C. Increased temperature, D. Increased BPG
B: Decreased CO2
Answer: B: Decreased CO2 
Explanation: Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2 and thus less delivery of O2 to tissues. Exercise causes increased 2,3 DPG.
Shift to left seen in
-        Increased pH
-        Decreased 2,3 DPG, temperature, PCO2
-        HbF (Fetal)
Shift to right seen in
-        Decreased pH
-        Increased 2,3DPG, temperature, PCO2
-        HbS (Sickle cell)