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: Pharmacology
[{'content': 'Calcium channel blocker with maximum effect on conduction in heart is: \nSelect and explain. \nA. Phenylamine, B. Nifedipine, C. Diltiazem, D. Verapamil', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]