Answer:
ok, so if an hiv is a virus that attacks the immune system, how does that affect you?
 if your immune system is weak in a moment, bad bacteria can enter your blood and cause problems and weaken your immune system even more. 
its really bad for a person's health, it weakens your immune system so your body has a tougher time fighting against a virus. 
 
        
                    
             
        
        
        
Human encroachment that has greatly reduced the prairie dog populations.  
        
                    
             
        
        
        
Answer:
Farms
laundry detergents 
pet wastes
Water treatment plants
Explanation:
Because its not construction materials or mining wastes.
 
        
                    
             
        
        
        
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.