Q: Fact 1: Amold spore has a negative impact on the respiratory system. Fact 2: Mold spores, for example, are microscopic. Given the two facts above, what can cause respiratory issues?

OPTIONS: 1. smoking tobacco. 2. a pathogens. 3. Microscopic organisms. 4. Normal humidity. 5. some viruses. 6. Clean air. 7. smoking pipes. 8. Mild weather.
A:
3.