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
[{'content': 'A travelling nerve impulse does not depolarize the area immediately behind it, because: \nSelect and explain. \nA. It is hyperpolarized, B. It is refractory, C. It is not self-propagating, D. The condition is always orthodromic', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. is \'b\' i.e. It is refractory Ganong writes -"Once initiated, a moving impulse does not depolarize the area behind it to the firing level, because this area is refractory"', 'role': 'assistant'}]