This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
Effect of fetal hemoglobin on O2 dissociation curve 
Select and explain. 
A. Right shift, B. Left shift, C. No effect, D. May be right or left
B: Left shift
Answer: B: Left shift 
Explanation: Oxygen dissociation curve is the graphic expression of the affinity of hemoglobin for oxygen as a function of the paial pressure of oxygen. Dissociation is influenced by pH, temperature, and carbon dioxide pressure. Formerly called oxyhemoglobin dissociation curve.Ref: Ganong&;s review of medical physiology,3red edition, page no:610