You are presented with the question "What harms the respiration system?" and the following answer choices: 
- Pollution
 - sweating
 - Pesticides
 - exercise
 - smoking
 - parasites
 - swimming
 - breathing

Now knowing that smoking causes direct damage to the lungs and mammals are warm blooded, use lungs for respiration, and have four legs, choose the best answer.


 

     smoking    