This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nerve Physiology, Subject name: Physiology
Which of the following nerve fibres is unmyelinated? 
Select and explain. 
A. A-alpha, B. A-beta, C. A-delta, D. C fiber
D: C fiber
Answer: D: C fiber 
Explanation: Ans. D. C fiberTypes of mammalian nerve fibres: -Fiber TypeFunctionMyelinationFiber Diameter(um)Conduction Velocity (m/s)Spike Duration (ms)Absolute Refractory Period (ms)AaProprioception; somatic motorMyelinated12-2070-120 AbTouch, pressureMyelinated5-1230-700.4-0.50.4-1AgMotor to muscle spindlesMyelinated3-615-30 AdPain, temperatureMyelinated2-512-30 BPreganglionic autonomicMyelinated< 33-151.21.2C, Dorsal rootPain, temperatureUnmyelinated0.4-1.20.5-222C,SympatheticPostganglionic sympatheticUnmyelinated0.3-1.30.7-2.322