An 18-month-old boy was referred to the pediatrics clinic because of persistent anemia and associated failure to thrive. Laboratory analysis confirmed a microcytic anemia and revealed blood lead levels of 50 mg/dL (2 times normal levels) and high levels of coproporphyrinogen III in the urine. The child was put on chelation therapy and recovered uneventfully. The cause of the child's difficulty was most likely due to the effects of the lead. The findings in this patient most closely reflect lead inhibition of which of the following enzymes of heme biosynthesis?a) δ-aminolevulinic acid (ALA) dehydrataseb) ferrochelatasec) porphobilinogen (PBG) deaminased) proporphyrinogen III cosynthasee) uroporphyrinogen decarboxylase