This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Medicine
A 73-year-old-woman presents to the clinic complaining of fatigue and feeling unwell. She notes the symptoms are worse on exertion, but denies any chest pain or shortness of breath. Her past medical history is significant for hypertension and type 2 diabetes. Both conditions are well controlled on her current medications. On physical examination, the vital signs are - blood pressure 135/80 mm Hg, pulse 72/min, and respiratory rate 10/min. The lungs are clear on auscultation and the heart sounds are normal. A CBC reveals a hemoglobin value of 9.5 g/dL and a MCV 105 mm3. Which of the following typically causes a macrocytic anemia? 
Select and explain. 
A. vegan diet, B. iron deficiency, C. thalassemia, D. chronic inflammation
A: vegan diet
Answer: A: vegan diet 
Explanation: A vegan diet (no meat, eggs, fish, cheese, and other animal products) can result in B12 deficiency. Iron deficiency, thalassemia, chronic inflammation, or sideroblastic anemia do not cause macrocytosis.