Answer:
A 
Explanation:
The darker moths would be harder for the bird to see due to the amount of soot on the trees. The darker moth population would thrive and continue to grow, while the lighter colored moth population would decrease. 
 
        
             
        
        
        
Answer and explanation;
-Aba is a suitable replacement because Aba and Cys have approximately the same sized side chain and are similarly hydrophobic. 
-However, Aba cannot form disulfide bonds so it will not be a suitable replacement if these are required. 
-Alpha-Aminobutyric acid is biosynthesized by transaminating oxobutyrate, a metabolite in isoleucine biosynthesis.
 
        
             
        
        
        
The answer i believe is d.
hope this helps!!!
        
                    
             
        
        
        
each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.