The variables are defined as the factors in an experiment, which are liable to change. The variable can be dependent or independent. The Independent variable is a variable, which is unaffected by the changes in the other variables. 
In this case, the brand of the food Shara feeds to the rats is independent factor, but it is changes in the system, so, it is an independent variable. 
The effect on the weight of the rat is dependent on the brand of food they are consuming. So, the weight of rats is dependent variable. 
 
        
                    
             
        
        
        
Answer:
we dont but when we fish in the reef it gives us more fish faster but people to lazy to take n' hour longer and not destroy the reef
Explanation:
 
        
                    
             
        
        
        
Answer:
A. DNA Polymerase
Explanation:
It absolutely cannot be C. Ozone or D. Radiation since those two answers are in relation to outside variables affecting health. Not inherited diseases. Therefore, it is in between A. or B. 
 
        
                    
             
        
        
        
Scientists carry out several researches to understand the cause and reason behind the natural phenomena happening around us. While carrying out an experiment, the scientist need to refer to various research papers and research articles to plan and follow the protocol of the experiment accordingly. 
Going through the background studies lead to greater insight and knowledge about the subject. It broadens our mind and way of thinking. It makes us more logical and precise towards our work.