Type of chocolate bar, size of it, surface it is placed on, etc
Controlled variables are anything that stay the same for both trials
        
                    
             
        
        
        
Because acids have a bitter taste i believe
        
                    
             
        
        
        
Narcotic drugs are analgesic that exert a depressing action on the central nervous system. 
Hope this helps!
        
             
        
        
        
Answer:
d) Protein
Chromatin fibres are wrapped around special proteins called Histones
Hope it helps you 
And pls mark it as the brainliest answer