Answer:oxygen, carbon, hydrogen, and nitrogen
Explanation: those are the four most important elements in all living thigns
 
        
             
        
        
        
Answer:
The two types of cells that never go through cell division once fully formed are nerve cells and muscle cells.
Explanation: 
The nerve cells and the muscle cells not undergo cell division after formation, because they can never re grow or cannot be repaired once they are mature. We should take good care of it once they are matured. They just under division from being baby to teenagers after that they stop undergoing cell division. This is true for both elephants as well as human beings. This thing is also applicable in case of bones. 
 
        
             
        
        
        
Answer:
In science, a variable is any item, factor, or condition that can be controlled or changed
 
        
             
        
        
        
Answer:
Entre ellas la más destacada y elaborada es la Hipótesis de la Automedicación que propone que los trastornos por dependencia de drogas son el resultado de la existencia de una alteración biológica
Explanation: