<prompt> A 50-year-old woman presents with easy fatigability, a smooth sore tongue, numbness and tingling of the feet, and weakness of the legs. A complete blood count shows a megaloblastic anemia that is not reversed by folate therapy. Hemoglobin is 5.6 gdL, WBC count is 5,100mL, and platelets are 240,000mL. This patient most likely has a deficiency of which of the following vitamins?Vitamin B1 thiamineVitamin B2 riboflavinVitamin B12Vitamin K  <response>: Except for a few rare situations, vitamin B12 cyanocobalamin deficiency is usually a result of pernicious anemia, an autoimmune disease of the stomach. Vitamin B12 is required for DNA synthesis, and its deficiency results in large megaloblastic nuclei.Diagnosis: Vitamin B12 deficiency, pernicious anemia 