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
In a patient of congenital prolonged QT syndrome and intermittent Torsades de pointes, which of the following should be prescribed: 
Select and explain. 
A. Magnesium sulphate, B. Metoprolol, C. Cardiac pacing, D. Isoprenaline
A: Magnesium sulphate
Answer: A: Magnesium sulphate 
Explanation: None