methods of filtering gasoline use of chlorofluorocarbons (CFCs) methods of radioactive waste storage use of mercury (Hg) compounds
I gave my students this multiple choice question: Which of these has been controlled in an attempt to reduce the depletion of ozone in Earth's atmosphere?

Only one answer is correct among these 4 choices:
- methods of filtering gasoline
- use of chlorofluorocarbons (CFCs)
- methods of radioactive waste storage
- use of mercury (Hg) compounds

Could you tell me which one is correct?

use of chlorofluorocarbons (CFCs)