Why Does Fetal Hemoglobin Have a Greater Affinity for Oxygen

Why does fetal hemoglobin have a greater affinity for oxygen than adult hemoglobin?

A) The fetus does not have its own oxygen supply and must rely on oxygen from the maternal vascular system.
B) The fetus has two g-chains on the hemoglobin, rather than two b-chains as in the adult.
C) Fetal hemoglobin interacts less readily with diphosphoglycerate (DPG) , which inhibits hemoglobin-oxygen binding.
D) Fetal hemoglobin production occurs in the vessels and liver rather than in the bone marrow as in the adult.