Thalassemia major (Cooley's anemia) is treated primarily with:

A. Oxygen therapy: Oxygen therapy may be used during acute complications but is not the mainstay of treatment. B. A diet high in iron: Iron overload is already a complication of repeated transfusions; high iron intake is contraindicated. C. Bed rest until the sedimentation rate is normal: Bed rest is not a specific treatment for thalassemia and ESR is not a key indicator for this condition. D. Multiple blood transfusions: Frequent transfusions are the primary treatment for thalassemia major to maintain normal hemoglobin levels and suppress ineffective erythropoiesis.