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: Unknown
[{'content': 'Digitalis does not affect which parameter of heart - \nSelect and explain. \nA. Heart rate, B. Contractility, C. Coronary blood flow, D. None of the above', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'D ' i.e., None of the above", 'role': 'assistant'}]