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Had (1) not been for the invention of CFCs (chlorofluorocarbons) in the 1920s, at least one environmental problem might have been avoided. In fact, (2) they to be invented today, they (3) no doubt be immediately banned. For fifty years, though, if you bought an air conditioner or a spray, there (4) a good chance that it contained CFCs - and those CFCs are still around in the atmosphere.
If you (5) able to travel into the upper layers of the atmosphere, you (6) , see the chlorine and fluorine from CFCs breaking down the ozone (a form of oxygen). Ozone could damage your lungs (7) you were to breathe it, but high in the atmosphere it performs the function of blocking ultraviolet rays from the sun, rays which can cause skin cancer if you (8) exposed to them. We might (9) have known about the process (10) it not been for the work of two American scientists, Frank Rowland and Mario Molina. A number of industries fought against their conclusions, and might have won (11) the evidence not been so clear. Rowland and Molina received the Nobel Prize for Chemistry in 1995 for their work on the ozone layer, but (12) which we might today be facing an even greater problem.
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