This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ECG, Subject name: Physiology
[{'content': 'When recording lead I on an ECG, the right arm is the negative electrode and the positive electrode is the \nSelect and explain. \nA. Left arm, B. Left leg, C. Right leg, D. Right arm + left leg', 'role': 'user'}, {'content': 'Answer: A \nExplanation: By convention, the left arm is the positive electrode for lead I of an ECG.', 'role': 'assistant'}]