Which of these is not a cause of rightward shift of Oxygen – Hemoglobin dissociation curve?

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)