Final answer:
The best prognosis for a child with acquired aplastic anemia is bone marrow transplantation.
Step-by-step explanation:
The best prognosis for a child diagnosed with acquired aplastic anemia is d. Bone marrow transplantation. A bone marrow transplant involves replacing the faulty bone marrow of a patient with healthy bone marrow from a donor. This procedure reconstitutes the patient's immune system and offers the best chance of survival for children with this condition.