Limits to variation The most obvious limit to natural selection is that suitable variation may not be available. This may be because certain phenotypes cannot be built, being ruled out either by physical law or by the properties of biological materials.
        
             
        
        
        
Answer:
D. trait formation due to behaviors
Explanation:
It is obvious to see that the three animals, cat, whale, and bat, have the same basic structure of their forelimbs, but also that they have developed differently and have taken a new shape. The reason for this is a trait formation due to behavior. The cats ancestors were terrestrial, and the cats have remained terrestrial, walking on their four legs, and having the same shape and function as their ancestors. The whales had similar forelimbs, but their ancestors started to move more and more in water. As they did, they needed more muscle power, but also greater width of the forelimb so that they can move more easily and more efficiently in the water. This behavior has gradually resulted in a flat, strong, peddle like forelimb. The bat too had similar forelimbs to that of the cat, but its ancestors started to try to fly. The process was gradual, and it started with jumping, then longer jumps, development of skin between the fingers, elongation of the fingers, thus provide more area for development of wider skin area. This has resulted in developing a light, wide, skin dominated forelimb with elongated fingers, providing flight for the bat.
 
        
             
        
        
        
Answer:
All cells have plasma membranes. Can molecules enter and leave the cell? Yes. The plasma membrane (also called the cell membrane), is a lipid barrier where molecule organelles live. The golgi ( a cell organelle) helps move the proteins across the plasma membarane. Proteins cannot move through the plasma membrane barrier by themselves because they are not small enough like water. 
Explanation:
Hope this helps. :) P.S. Can I be marked brainliest . . . ? :)
 
        
             
        
        
        
Answer:
D, 'cus Heterotrophs can't make their own food like plants or humans, and Autotrophs can make their own food. For example plants, or in this case bacteria
 
        
                    
             
        
        
        
Answer:
All parasympathetic target organs