Q. A 46-year-old man presents to outpatient follow-up with symptoms of sluggishness and shortness of breath with simple activities. He reports that he used to be able to walk a few miles with his wife in the evenings without issue but now he struggles going a few blocks without getting "winded". On clinical examination, you notice that he appeals more pale than in prior visits. You also appreciate that he has a smooth appearing tongue. Neurological examination is normal. You are concerned about him having anemia. You send a variety of blood tests, which demonstrate a hemoglobin level of 10 mg/dl, an elevated homocysteine level, and a normal methylmalonic acid level. A blood smear shows neutrophils with 5 to 6 lobes and large RBCs. In the table below, which of the following rows is consistent with this patient's most likely diagnosis?