<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 6-year-old boy is brought to the emergency department with a mild fever for the past week. He has also had generalized weakness and fatigue for the past month. He has been complaining of diffuse pain in his legs and arms. He has a history of Down syndrome with surgical repair of a congenital atrial septal defect as an infant. His temperature is 38.0 C 100.4 F, pulse is 85min, respirations are 16min, and blood pressure is 9060 mm Hg. He has enlarged cervical lymph nodes bilaterally that are nontender to palpation. He is uncooperative for the rest of the examination. Laboratory studies show:Hemoglobin 10.2 gdLHematocrit 30.0Leukocyte count 50,000mm3Platelet count 20,000mm3SerumSodium 136 mEqLPotassium 4.7 mEqLChloride 102 mEqLBicarbonate 25 mEqLUrea nitrogen 18 mgdLCreatinine 1.1 mgdLTotal bilirubin 0.9 mgdLAST 30 ULALT 46 ULWhich of the following is most likely to confirm the diagnosis?? A: Monospot test, B: Blood culture, C: Echocardiography, D: Bone marrow biopsy, E: Serum protein electrophoresisn,  <response>: Based on the information provided in the question stem, this appears to be a case of a 6-year-old boy with Down syndrome presenting with fever, fatigue, generalized pain, and lymphadenopathy. His lab results show pancytopenia low hemoglobin, hematocrit, and platelets, elevated liver enzymes, and leukocytosis with a left shift. The key finding is pancytopenia, which indicates bone marrow suppression. This, along with the lymphadenopathy and elevated liver enzymes, points towards a diagnosis of leukemia, likely acute lymphoblastic leukemia ALL, which is common in children with Down syndrome.The answer choices provide different diagnostic tests. A monospot test detects heterophile antibodies seen in mononucleosis - this is incorrect. Blood cultures would not confirm leukemia. Echocardiography may detect cardiac abnormalities but would not confirm this diagnosis. A bone marrow biopsy is the definitive test to evaluate marrow cellularity and confirm leukemia. Serum protein electrophoresis evaluates monoclonal gammopathies seen in multiple myeloma - this is irrelevant here.Therefore, a bone marrow biopsy is the best answer. It would allow examination of bone marrow under microscopy and confirm the diagnosis of leukemia.D: Bone marrow biopsy 