1. A 22-year-old m an com plained to his physician of increasing fatigue, anorexia, and irritability over the past 2 m onths. The m an had been su ering from gluten enteropathy since his infancy....

1. A 22-year-old m an com plained to his physician of increasing fatigue, anorexia, and irritability over the past 2 m onths. The m an had been su ering from gluten enteropathy since his infancy. Physical exam ination revealed pallor, glossitis, paresthesias, and m uscle weakness. Pertinent laboratory values were red blood cell count (RBC) 3.4 × 106/mm3 (norm al, m ale 4.3-5.9 × 106/mm3), m ean corpuscular volum e 116 fL (normal 80-100 fL), serum vitam in B12 330 pg/m L (norm al > 280 pg/m L), serum ferritin 200 ng/m L (norm al 30-300 ng/m L). Blood stain showed m acro-ovalocytic red blood cells and hypersegm entation of neutrophils. An appropriate drug was started, and 10 days later, the RBC w as norm al. W hich of the follow ing actions m ost likely m ediated the therapeutic e ect of the drug in the patient’s disease? A. Increased conversion of hom ocysteine to m ethionine B. Increased synthesis of tetrahydrofolate C. Increased absorption of iron from duodenal m ucosa D. Decreased erythrocyte destruction E. Increased synthesis of erythropoietin