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: Radiology
[{'content': 'CT scan shows a suharachnoid haemorrhage following symptoms of sudden headache and paralysis. Next investigation of choice is: \nSelect and explain. \nA. 4-vessel angiography, B. SPECT, C. Transacromial Doppler USG, D. MRI', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. 4-vessel angiography', 'role': 'assistant'}]