I would say C. Why I say this is because fur is used to keep an animal warm. If the animal no longer needs to be kept warm, then it no longer needs the thick fur. 
        
                    
             
        
        
        
Answer:
I believe the answer is A) energy pyramid
Explanation:
It's talking about trophic levels, as opposed to individual organisms.
 
        
                    
             
        
        
        
One of the possible answers is sickle cell.
 
        
        
        
Answer:
C, a long absolute refractory period.
Explanation:
Tetanus is not possible in cardiac muscle tissue because cardiac cells have longer action potentials and a very long refractory period compared to other cells. This helps prevent the heart from cramping and seizing up.
 
        
             
        
        
        
Is size exclusion chromatography one of the choices?