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 nondiabetic, non hypertensive adult male develops sudden severe headache with altered sensorium,likely diagnosis is - \nSelect and explain. \nA. Brain tumour, B. Subarachnoid haemorrhage, C. Encephalitis, D. Meningitis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]