I believe runoff would be the answer.
        
                    
             
        
        
        
1. Two genetically identical copies of DNA 
2. Finds an error in DNA, removes the incorrect nucleotide and replaces it with a correct one.
3. It is used as a copy/ "template" for replication in order to have two identical copies of DNA.
4. DNA helicase unwinds DNA double helix and Topiosomerase ensure there isn't too much unwinding.
5. Replication has a built on proofreading system - DNA polymerase removes the incorrect nucleotide and replaces it with a correct one.
        
             
        
        
        
Food is a basic need for all organisms
        
                    
             
        
        
        
Answer:
Different brands of nail polishes used by Sarah.
Explanation:
While conducting an experiment two different variables are considered namely dependant variable and independent variable. The variable which is continuously changed to see the effects is called as independent variable and the variable which is being tested is called as dependant variable. 
In the given scenario, Sarah want to know best brand of nail polishes which lasts longest without chipping. Thus the different brands of nail polish used by her is considered as independent variable.