Probably grow back neurons of those affected by dementia, <span>Parkinson's, 
</span><span>Huntington's and other diseases that destroy neurons.</span>
        
             
        
        
        
Answer:
The correct answer is 
18
Groups of the periodic table: The s-, p-, and d-block elements of the periodic table are arranged into 18 numbered columns, or groups.
Hope this helps! 
- Quinn <3