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': "A patient presents with melaena. normal renal function, hypertension and mononeuritis multiples. The most probable diagnosis is \nSelect and explain. \nA. Classical polyarteritis nodosa, B. Microscopic polyangiitis, C. Henoch-Schonlein purpura, D. Buerger's disease", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]