Why Are Infants With $\beta$ -Thalassemia Major Not Ill Until Approximately 6 Months of Age

Why are infants with $\beta$ -thalassemia major not ill until approximately 6 months of age?

A) Infants are protected by their high concentration of Hb F.
B) Infants have less need for hemoglobin because of their small body size.
C) Infants have less need for hemoglobin because of their smaller lung capacity.
D) Infants have a high red count and thus higher hemoglobin from a higher than normal concentration of erythropoietin.