This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': "Kaposi's sarcoma is a tumour of: \nSelect and explain. \nA. Blood vessels, B. Reticuloendothetial system, C. Striated muscles, D. Smooth muscles", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]