When the Patient with Pernicious Anemia Says,"I Don't Know Why

When the patient with pernicious anemia says,"I don't know why I am so tired," the nurse can clarify by saying that the fatigue is related to:

A) lack of oxygen being carried to cells of the body.
B) enlarged spleen, which makes breathing difficult.
C) proliferation of white cells.
D) excessive red cells that have decreased the blood pressure.