The following are multiple choice questions (with answers) about medical knowledge.   **Question:** A 6-year-old boy is brought to the physician because of abdominal distention, fatigue, and night sweats over the past 4 months. He also has a 2-month history of post-prandial fullness and recurrent nonbilious vomiting. He appears pale. Abdominal examination shows hepatosplenomegaly and shifting dullness; there is mild tenderness to palpation. Examination of the skin shows multiple nonblanching maculae. A CT scan of the abdomen shows mesenteric and retroperitoneal lymph node enlargement and nodular thickening of the omentum. A photomicrograph of a biopsy specimen from an enlarged mesenteric lymph node is shown. Immunohistochemical staining of the Ki-67 nuclear antigen shows that the proliferation index of the specimen is > 99%. The structure indicated by the arrows is most likely which of the following?   (A) Neutrophil   (B) Human immunodeficiency virus   (C) B lymphocytes   (D) Macrophage
['(D) Macrophage <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Neutrophil \n (B) Human immunodeficiency virus \n (C) B lymphocytes \n (D) Macrophage <> possible answers', '  A 6-year-old boy is brought to the physician because of abdominal distention, fatigue, and night sweats over the past 4 months. He also has a 2-month history of post-prandial fullness and recurrent nonbilious vomiting. He appears pale. Abdominal examination shows hepatosplenomegaly and shifting dullness; there is mild tenderness to palpation. Examination of the skin shows multiple nonblanching maculae. A CT scan of the abdomen shows mesenteric and retroperitoneal lymph node enlargement and nodular thickening of the omentum. A photomicrograph of a biopsy specimen from an enlarged mesenteric lymph node is shown. Immunohistochemical staining of the Ki-67 nuclear antigen shows that the proliferation index of the specimen is > 99%. The structure indicated by the arrows is most likely which of the following? <> context@']