This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'In a normal electrocardiogram (ECG or EKG), \nSelect and explain. \nA. The P wave results from repolarization of the atria., B. The QRS complex results from depolarization of the ventricles., C. The T wave represents repolarization of the auricles., D. During the P-R interval, the ventricle contract.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B:\xa0The QRS complex consists of three individual waves: the Q, R, and S waves. The QRS complex results from depolarization of the ventricles, and the beginning of the QRS complex precedes ventricular contraction.\nA:\xa0The P wave results from depolarization of the atrial myocardium, and the beginning of the P wave precedes the onset of atrial contraction.\nC:\xa0The T wave represents the repolarization of the ventricles, and the beginning of the T wave precedes ventricular relaxation.\nD:\xa0During the P-R interval, the atria contract and begin to relax.', 'role': 'assistant'}]