The food chains make up the food webs
        
             
        
        
        
Answer:
So they are lighter and move quicker. 
Explanation:
With the small wings and bodies birds have it would be hard for them to escape predators and lift their own weights if their bones were dense like humans' bones. The hollow part of the birds' bone is connected to their lungs so they have enough oxygen to fly easily. Hope this can help you! :)
 
        
             
        
        
        
The answer is d. all of the above. The amount of nitrogen in the atmosphere can be affected by the inorganic nitrogen fertilizers, sewage treatment plants and pollution coming from factories. Hope this is the answer and this would be of help.
        
                    
             
        
        
        
B. They decrease water absoption
        
             
        
        
        
<span>The male's feathers do not get longer and longer each generation because they would reach a point in which the feathers would hinder their survival. If the females preferred feather trains that would help males fly, then males would likely have much shorter feather trains.</span>