1. eating healthy foods.
2. getting enough sleep.
3. getting enough exercise
4. managing stress
5. washing your hands consistently.
All of those things helps your immune system by strengthening it or by keeping germs away which intern helps prevent you from getting sick.
I hope this helps. Let know if anything is unclear.
3 is the answer. This harms the lungs. Nicotine can cause lung damage less fast than tobacco.
Oxidative stress is an imbalance between the production of free radicals (highly unstable molecules that are naturally formed when you exercise and when your body converts food into energy) and the ability of the body to counteract or detoxify their harmful effects through neutralization by antioxidants. Antioxidants such as thiols or ascorbic acid prevent free radicals forming due to oxidation. Some ways our bodies can be exposed to oxidative stress are by having an unbalanced diet, smoking, or sun exposure. Some ways to prevent oxidative stress are having a healthy diet, not smoking, exercising regularly and wearing sunscreen.