You are presented with the question "What can cause respiratory issues?" and the following answer choices: 
- smoking tobacco
 - a pathogens
 - Microscopic organisms
 - Normal humidity
 - some viruses
 - Clean air
 - smoking pipes
 - Mild weather

Now knowing that amold spore has a negative impact on the respiratory system and mold spores, for example, are microscopic, choose the best answer.


 

   Microscopic organisms      