BCH4024 OC SP26 E3 Q48: A7‑mоnth‑оld infаnt is evаluаted fоr poor growth and anemia that does not improve with iron supplementation. Family history is unknown. On examination, the infant is small but otherwise appears healthy, with normal muscle tone and reflexes. A bone marrow smear shows marked megaloblasts (large, immature red blood cell precursors). Urinalysis reveals markedly increased excretion of orotic acid. Dietary supplementation with which of the following compounds is most likely to improve this infant’s anemia and growth?