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: Medicine
[{'content': 'Hypersensitivity vasculitis affects - \nSelect and explain. \nA. Post-capillary venules, B. Arterioles, C. Veins, D. Medium-sized arteries', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]