The Terminal Ileum Was Removed from a

The terminal ileum was removed from a
50-year-old woman during excision of a tumor. About 3 years later, the patient was admitted to the hospital. She is very pale. Hemoglobin is 9 g/dL, MCV (mean corpuscular volume) has increased to 110 mm3 (110 fL) . The provisional diagnosis is a vitamin deficiency. Which of the following vitamins is the most likely one causing the symptoms?

A) A
B) B₁
C) B₆
D) B₁₂
E) K