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
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 - 
Select and explain. 
A. Flurocarbons, B. Salbutamol, C. Ozone, D. Oxygen
A: Flurocarbons
Answer: A: Flurocarbons 
Explanation: None