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': 'Patients with atrial fibrillation have \nSelect and explain. \nA. Regular irregular pulse, B. Irregularly irregular pulse, C. Anacrotic pulse, D. Pulsus alternans', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]