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': 'True about fourth heart sound is \nSelect and explain. \nA. Occurs at end of P wave in ECG, B. Occurs at end of T wave in ECG, C. Occurs during early rapid filling phase of ventricular diastole, D. Occurs during slow ejection phase of Ventricular systole', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]