Carbon dioxide is what humans exhale, giving trees carbon dioxide will produce oxygen 
 
        
                    
             
        
        
        
B) they work independently of one other
        
                    
             
        
        
        
Because it helps the environment strive and keep its self alive my controlling populations and bringing in new ones
        
             
        
        
        
To gather data or information or to observe. HOPE THIS HELPS!! IF SOO LET ME KNOOW