You have to first make some observations and then ask a question. Then you make a hypothesis (or guess) what the answer is - do the experiment to see if you're right!
 
        
             
        
        
        
Function of integumentary system: PROTECTION<span>- barrier against infectious, chemical, radioactive, and physical damage.
- keratin and junctions block bacteria, fungi, and blunt objects.
-macrophages identify foreign particles and activate immune response.</span>
        
             
        
        
        
Answer:
The cilia is one of the things that act defensively in the respiratory system. 
Explanation:
It propels a mucus-like liquid that covers the airway which traps pathogens (potentially infectious microorganisms) and other particles, preventing them from reaching the lungs.
 
        
             
        
        
        
A- uracil, test prep question