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
A nondiabetic, non hypertensive adult male develops sudden severe headache with altered sensorium,likely diagnosis is - 
Select and explain. 
A. Brain tumour, B. Subarachnoid haemorrhage, C. Encephalitis, D. Meningitis
B: Subarachnoid haemorrhage
Answer: B: Subarachnoid haemorrhage 
Explanation: None