Answer: d. assimilating the nitrogen into their own biomolecules.
Explanation: I just had this question for an assignment. 
Hope this helps!  :)
 
        
             
        
        
        
Answer : B is the heaviest puppy amongst all.
Explanation : There are three comparisons shown in the figure, out of which B is assumed to be heaviest amongst all on the basis of following assumptions.
When weighing A and C puppy, A was found to have lighter weight than C. So, in this case C is the heavier puppy.
In second case, when C and D are weighed, both are found to be equal in weight.
Then last comparison was with B and D puppies where, D was observed to be of light weight and B proved to be the heaviest.
Therefore, the conclusion is that B is the heaviest puppy in comparison with rest others.
 
        
                    
             
        
        
        
They were completely heterophic in nature because it allowed them to absorb different material from the environment as an energy source