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': 'Causes of water-hammer pulse  are \nSelect and explain. \nA. Truncus arteriosus, B. Patent ductus arteriosus, C. Both, D. None', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Water hammer pulse (collapsing pulse) is seen\xa0in:\n\nHyperkinetic circulatory states\nAortic regurgitation\nPatent ductus arteriosus\xa0\nTruncus arteriosus with truncal sufficiency', 'role': 'assistant'}]