There is a change in amino acids sequence causes these mutations, If there is an error in the order of amino acids during the process of multiplication, there is a special enzyme to repair errors 
        
             
        
        
        
Answer; 
Decreased birthrate 
If immigration and emigration numbers remain equal , decreased birthrate could cause a slowed growth rate. 
Explanation; 
All populations change in size with time . Change in population is dependent of various factors, namely; birthrates, death rates, immigration and emigration. 
Therefore; change in population size would be given by the difference of the sum of birth rates and immigration and the sum of death rates and emigration. That is; Change in Population Size = (Births + Immigration) - (Deaths + Emigration). A decreased birth rate with emigration and immigration remaining constant would cause a slowed growth rate.
 
        
                    
             
        
        
        
I would have to say d.Please let me know if i am right.
        
                    
             
        
        
        
That is called Urogenital myiasis which is a parasitic infestation. These flies are in the Diptera species group and the cause of this myiasis is from the eggs and larvae of this species (fly). 
Let me know if you need further info. 
                - Dotz