22. We know that tobacco is harmful to the circulatory system because it 1. Is linked to heart disease.
2. Destroys red blood cells.
3. Decreases heart rate.
4. Strengthens the respiratory system.
22 Whatiana

1. Is linked to heart disease

Explanation:

We automatically rule out numbers 3 and 4 because smoking tobacco actually INCREASES heart rate and weakens the respiratory system. Also, we are talking about the circulatory system, so we automatically know it has something to do with the heart. There is definitely a link to heart disease and this is a lot more devastating than red blood cells. So I'd go with 1, unless your teacher taught you otherwise.

answer; indirect elisa;