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
Most common post-operative complication of spinal anaesthesia ? 
Select and explain. 
A. Post-spinal headache, B. Hypotension, C. Meningitis, D. Urinary retention
A: Post-spinal headache
Answer: A: Post-spinal headache 
Explanation: Ans. is 'a' i.e., Post-spinal headache