This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'The basis of Korotkoff sound is \nSelect and explain. \nA. Aoic valve closure, B. Production of hea sound, C. Aerial turbulence, D. Aerial valve expansion', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The sounds of Korotkoff are produced by turbulent flow in the brachial aery. When the aery is narrowed by the cuff, the velocity of flow through the constriction exceeds the critical velocity and turbulent flow results.', 'role': 'assistant'}]