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: Physiology
[{'content': 'Isovolumetric relaxation phase of the cardiac cycle ends with \nSelect and explain. \nA. Peak of C waves, B. Opening of AV valve, C. Closure of semilunar valve, D. Beginning of T waves', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]