This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Conducting System of Hea, Subject name: Physiology
[{'content': 'Slowest conducting pa in the hea is: \nSelect and explain. \nA. SA node, B. AV node, C. Atrial fibers, D. Bundle branches', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Both SA node and AV node contain slowly depolarizing cells. Both of them conduct impulse slowly. Velocity of impulse through both SA node and AV node is about 0.05 - 0.1 sec. In addition, AV node has 2 more propeies: Small diameter of fibers Fewer gap junctions between adjacent cells. These features make the AV node even slower in conducting the impulse.', 'role': 'assistant'}]