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: Anaesthesia
[{'content': 'Onset of post spinal headache is usually at hours after spinal anesthesia \nSelect and explain. \nA. 0 - 6, B. 12-Jun, C. Dec-72, D. 72 - 96', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., 12 - 72", 'role': 'assistant'}]