This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
[{'content': 'Which of the following drugs has been found to be useful in acute severe asthma ? \nSelect and explain. \nA. Magnesium Sulphate, B. Anti-leukotrine, C. Cromolyn Sodium, D. Cyclosporine', 'role': 'user'}, {'content': "Answer: A \nExplanation: A high concentration of oxygen should be given by face mask to achieve oxygen saturation of >90%.Magnesium sulfate given intravenously or by nebulizer has been found to be effective in acute severe asthma,when added to inhaled beta2 -agonists & is well tolerated.It can provide additional bronchodilation in patients whose presenting PEF(peak ejection fraction)is below 30% predicted. Reference:Harrison's medicine-18th edition,page no:2113;Davidson's medicine-22nd edition,page no:672.", 'role': 'assistant'}]