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': 'First fibres to be blocked in spinal anaesthesia is: \nSelect and explain. \nA. Sympathetic preganglionic, B. Afferent motor nerves, C. Sensory fibres, D. Different motor nerves', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Sympathetic preganglionic', 'role': 'assistant'}]