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: Medicine
[{'content': "One of the constituents of the commonly used metered dose inhalers in bronchial asthma which is an air pollutant & dangerous to earth's stratosphere is - \nSelect and explain. \nA. Flurocarbons, B. Salbutamol, C. Ozone, D. Oxygen", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]