Answer:
carbonic acid
Explanation:
carbondioxide reacts with water in a reversible reaction to form carbonic acid
 
        
             
        
        
        
The optimal pH can be measured by looking at enzyme activity verses pH. Enzyme activity will increase up to a certain pH; above that pH, the enzyme activity will begin to fall.
        
                    
             
        
        
        
Answer:
the correct answer is a 
ARE BASED ON A SET OF OBSERVATIONS 
hope this helps!