Fact 1: Smoking causes direct damage to the lungs. Fact 2: Mammals are warm blooded, use lungs for respiration, and have four legs. Given the two facts above, what harms the respiration system?

Available choices:
[+] Pollution;
[+] sweating;
[+] Pesticides;
[+] exercise;
[+] smoking;
[+] parasites;
[+] swimming;
[+] breathing;
Answer:
smoking