This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Which of the following nerve fibre is unmylenated? 
Select and explain. 
A. A-aplha, B. A-beta, C. A-delta, D. C fiber
D: C fiber
Answer: D: C fiber 
Explanation: C fibres are unmyelinated fibres and they are the slowest ones to conduct an impulse.Ref: Ganong&;s review of medical physiology; 23rd edition; pg:88