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: Physiology
[{'content': 'The nerve fibres having the largest diameter: \nSelect and explain. \nA. Somatic motor A alfa fibres., B. Preganglionic autonomic type B fibres., C. Dorsal root C fibres., D. Motor fibres A gamma fibres.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Somatic motor A alfa are the largest fibres in diameter with a diameter of 12-29microns.', 'role': 'assistant'}]