<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 32-year-old man presents with a 2-month history of increasing lethargy, frequent upper respiratory tract infections, and easy bruising. Past medical history is unremarkable. The patient reports a 14-pack-year smoking history and says he drinks alcohol socially. No significant family history. His vital signs include: temperature 36.8C 98.2F, blood pressure 13291 mm Hg and pulse 95min. Physical examination reveals conjunctival pallor and scattered ecchymoses on the lower extremities. Laboratory results are significant for the following:Hemoglobin 8.2 gdLLeukocyte count 2,200mm3Platelet count 88,000mm3Reticulocyte count 0.5A bone marrow biopsy is performed, which demonstrates hypocellularity with no abnormal cell population. Which of the following is the most likely diagnosis in this patient? ? A: Aplastic anemia, B: Myelodysplastic syndrome, C: Infectious mononucleosis, D: Acute lymphocytic leukemia, E: Drug-induced immune pancytopenia,  <response>: This is a clinical case of a 32-year-old man with symptoms of fatigue, frequent infections, and easy bruising. He has a normal past medical history and social alcohol use, but a 14 pack-year smoking history. On exam he has pallor and bruising. Lab tests show pancytopenia low hemoglobin, leukocytes, platelets, and reticulocytes. A bone marrow biopsy shows hypocellularity without abnormal cells. The pancytopenia with a hypocellular bone marrow points towards a disorder of decreased bone marrow production of blood cells. The normal bone marrow cellularity excludes leukemia and myelodysplasia. The lack of abnormal cells also makes these less likely. Infectious mononucleosis would present with lymphocytosis rather than pancytopenia. Drug-induced pancytopenia is possible given his smoking history, but the hypocellular marrow makes aplastic anemia most likely.A: Aplastic anemia 