This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
[{'content': 'The lead of ECG marked as X is called? \nSelect and explain. \nA. Lewis lead, B. V4R, C. aVR, D. Vg', 'role': 'user'}, {'content': 'Answer: B \nExplanation: And. B. V4R15 - Lead ECGV4R - 5th intercostal space midclavicular line (same as V4 but on the other side)V8 - On the back, 5th intercostal space midscapular line.V9 - On the Back, 5th intercostal space between V8 and the spine', 'role': 'assistant'}]