Answer:
natural selection I guess
 
        
             
        
        
        
Neuroglial Cells is the answer
        
             
        
        
        
There are four main types of tissue: muscle, epithelial, connective and nervous. Each is made of specialized cells that are grouped together according to structure and function. Muscle is found throughout the body and even includes organs such as the heart. Our outer layer of skin is epithelial tissue.
        
             
        
        
        
Answer:
Independent variable: The amount of fertilizer.
Dependent Variable : The amount of water, the amount of soil. amount of sun light.
Explanation:
I can't really explain it but I am pretty sure that is the right answer. Hope it helps :)