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: Forensic Medicine
[{'content': 'Commonest cause of thunderclap headache: AIIMS 10; NIMHANS 14 \nSelect and explain. \nA. Extradural hemorrhage, B. Aneursymal SAH, C. Subdural hemorrhage, D. Basilar migraine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Aneursymal SAH', 'role': 'assistant'}]