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': 'The ‘a’ wave in venous waveform is absent in case of \nSelect and explain. \nA. AV dissociation, B. Atrial fibrillation, C. Tricuspid incompetency, D. All of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]