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': 'In a patient of congenital prolonged QT syndrome and intermittent Torsades de pointes, which of the following should be prescribed: \nSelect and explain. \nA. Magnesium sulphate, B. Metoprolol, C. Cardiac pacing, D. Isoprenaline', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]