Answer:
Trees and plants.
Explanation:
Trees give us oxygen and plants get rid of carbon dioxide and remake it as oxygen.
 
        
                    
             
        
        
        
D - an increase in tree cover in the tundra. 
 
        
                    
             
        
        
        
These are sensor, registry and short-term memory.
        
             
        
        
        
Answer:
the answer to this is A. true