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
During exercise, increase in O2 delivery to muscles is because of all except 
Select and explain. 
A. Oxygen dissociation curve shifts to left, B. Increased stroke volume, C. Increased extraction of oxygen from the blood, D. Increased blood flow to muscles
A: Oxygen dissociation curve shifts to left
Answer: A: Oxygen dissociation curve shifts to left 
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)