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 blockers are not useful in: \nSelect and explain. \nA. Arrhythmia., B. Angina., C. Hypertension., D. Sick sinus syndrome.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Calcium channel blockers and beta-blockers are contraindicated in sick sinus syndrome.', 'role': 'assistant'}]