I believe it would be (B) but i’m sorry if i am wrong.
        
                    
             
        
        
        
Answer:
A dolphin or whale. 
Explanation:
It is a mammal, but is mistaken for a fish since it lives in the water. 
 
        
             
        
        
        
No new substance is produced.
        
             
        
        
        
The invading bullfrogs ARE HARMFUL. This is because, they cause decline in the population of the native species.
Decline in the population of the native species will throw the ecosystem into a condition of imbalance which will eventually affect all the living organisms that are living in that ecosystem.