The correct answer is a nutrient runoff.  
Nutrient runoff is a major reason for eutrophication of surface waters, in which extra amount of nutrients, generally phosphorus or nitrogen, instigate growth of algae. Sources of nutrient pollution involve surface runoff from pastures and farm fields, emissions from combustion, and discharges from septic tanks.  
 
        
                    
             
        
        
        
The statement which best explains why carbon is present in so many kinds of molecules is because <u>it can form four covalent bonds.
<em /></u>It isn't rare on Earth, so A is incorrect. It has valence electrons, so C is incorrect. It cannot become an ion, so D is incorrect.<u>
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Its important because it tells us the difference between populations and individuals
        
             
        
        
        
It's B
Explanation:
Because the fossil record shows how organisms have evoluate from relatively simple organisms to more complex organisms
 
        
                    
             
        
        
        
A. the mitochondria and chloroplasts are much different in structure than bacteria