This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ECG and Arrhythmia 3, Subject name: Medicine
[{'content': 'Which of the following can be used to calculate hea rate from an ECG? \nSelect and explain. \nA. Number of large squares in one R-R interval/300, B. 300/ (Number of large squares in one Q-T interval), C. 300/ (Number of large squares in one R-R interval), D. (Number of large squares in one Q-T interval) / 300', 'role': 'user'}, {'content': 'Answer: C \nExplanation: For calculating hea rate: HR-300/ Number of large squares(0.20 secs) in one R-R interval HR-1500/no of small squares (0.04 secs) in one R-R interval', 'role': 'assistant'}]