Answer:
This question is incomplete; the complete part is: what are the independent, dependent, and controlled variables?
Independent variable: ORGANIC AND CHEMICAL FERTILIZERS
Dependent variable: HEIGHT OF PLANT
Controlled variable: Same type of seed, water
Explanation:
Independent variable is the variable that is changed or manipulated by the experimenter. In this question, John wanted to test the effects that organic and chemical fertilizers had on plant growth. Hence, the independent variable is the ORGANIC AND CHEMICAL FERTILIZERS used. 
Dependent variable is the variable that responds to changes made to the independent variable. The dependent variable is the variable that is measured in an experiment. In this case, the HEIGHT OF PLANTS MEASURED is the dependent variable. 
Controlled variable or Constant is the variable that is kept unchanged throughout the experiment in order not to influence the experimental result or outcome. In this case, the controlled variable is the SAME TYPE OF SEED USED, WATER.
 
        
             
        
        
        
I believe the answer is B, the survival of the fittest due to competition for resources. Survival of the fittest is a term that originated from Darwinian evolutionary theory was a way of describing the mechanism of natural selection. The biological concept of fitness is  defined as reproductive success. Many organism overproduce to increase chances of survival for their organisms due to competition. 
        
                    
             
        
        
        
I’m not sure I think it’s D.) Hope I could help :))) 
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