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
[{'content': 'Group B fibers are: \nSelect and explain. \nA. Sympathetic preganglionic, B. Sympathetic postganglionic, C. Parasympathetic postganglionic, D. All', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Group B fibers are preganglionic fibers .. They are myelinated Ref:Guyton and Hall textbook of medical physiology 12th edition,page number: 73', 'role': 'assistant'}]