Because the environment is faster then the squrrel has to find stuff for the nest and a safe spot
        
                    
             
        
        
        
Endocrine system is the answer
        
             
        
        
        
It’s not the most visible by your picture. The correct answers are where the highest point of each line is because that is where the enzyme is working most efficiently. 
Here are my answers but because of the unclear image , please check them with my explanation above:
Pepsin. = pH2
Salivary Enzyme = pH7
Trypsin = pH9