Fish definitely have a central nervous system! 
It contains their brain, spinal cord and Medulla Oblongata (which is a connecting the brain with the spinal cord!)
Their brains even have the same parts as the human brain! For example, they also have a cerebellums
        
                    
             
        
        
        
Answer:
cancer
Explanation:
Cancer can disrupt the cell cycle. Cancer is unchecked cell growth. Cell cycle is the process in which cells progress and divide. Mutations (random and sudden spontaneous changes) in genes can cause cancer by accelerating cell division rates or inhibiting normal controls on the system, such as cell cycle arrest or programmed cell death.
 
        
             
        
        
        
D.) ovary oviduct uterus then vagina 
 
        
             
        
        
        
The pituitary gland is known as the "master gland" because it is known to control hormones that regulate several other important systems in the endocrine system such as the thyroid gland, ovaries, and testes.
        
             
        
        
        
The effects could be, the top consumers may run out of food, which would make it harder for them to catch food