This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
[{'content': 'In the cardiac cycle diagram, when does the first hea sound occur \nSelect and explain. \nA. Point A, B. Point B, C. Point C, D. Point D', 'role': 'user'}, {'content': 'Answer: A \nExplanation: When ventricle begin to contract isovolumetrically the mitral & tricuspid valves close producing First hea sound Ref: Metting, Physiology pretest and review, 14th edition', 'role': 'assistant'}]