This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ECG and Arrhythmia 3, Subject name: Medicine
[{'content': 'Most common arrhythmia: \nSelect and explain. \nA. Inappropriate sinus tachycardia, B. Junctional premature complexes, C. Atrial fibrillation, D. Atrial flutter', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]