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: Pharmacology
[{'content': 'Most common post-operative complication of spinal anaesthesia ? \nSelect and explain. \nA. Post-spinal headache, B. Hypotension, C. Meningitis, D. Urinary retention', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Post-spinal headache", 'role': 'assistant'}]