You are answering a USMLE-style medical question. Question: A 2-year-old boy is brought to the physician for evaluation of pallor and increasing lethargy for 2 days. One week ago, he experienced abdominal pain, vomiting, and bloody diarrhea that have since subsided. The patient's father states that they returned early from a 6-week roadtrip in Mexico because of these symptoms. His parents have been giving him oral rehydration solution. His immunizations are up-to-date. He appears pale. His temperature is 38.4°C (101.1°F), pulse is 130/min, respirations are 35/min, and blood pressure is 95/50 mm Hg. Examination shows scleral icterus. The abdomen is soft and nontender; there is no rebound or guarding. Bowel sounds are hyperactive. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 8.5 g/dL Mean corpuscular volume 94 μm3 Leukocyte count 18,000/mm3 Platelet count 45,000/mm3 Prothrombin time 12 sec Partial thromboplastin time 34 sec Serum Urea nitrogen 28 mg/dL Creatinine 1.6 mg/dL Bilirubin Total 2.5 mg/dL Direct 0.1 mg/dL Lactate dehydrogenase 1658 U/L A blood smear shows schistocytes. Which of the following is the most likely diagnosis?" Options: A) Henoch-Schönlein Purpura B) Thrombotic thrombocytopenic purpura C) Hemolytic uremic syndrome D) Immune thrombocytopenic purpura Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.