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
The factor responsible for the left shift of Hb-O2 dissociation curve is 
Select and explain. 
A. Increase in 2, 3 DPG in RBC, B. Fall in temperature, C. Fall in pH, D. Increase level of CO2 blood
B: Fall in temperature
Answer: B: Fall in temperature 
Explanation: Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2 and thus less delivery of O2 to tissues.
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)