B, proton is positive and it does not represent the symbol
        
             
        
        
        
Answer:
l think the suitable answer can be no.A. and no.D.
 
        
             
        
        
        
Answer:
?WHAT
Explanation:
class is this for ? 
and pls this doesnt make sense 
 
        
             
        
        
        
Answer:
A) they help transport some substances through the membrane. 
Explanation:
The membrane proteins that span the bilayer of phospholipids help in the transport of polar, large and charged substances across the membrane. The nonpolar core of the membrane does not allow these charged and polar substances to pass through. Proteins serving as channels form pores to allow movement of the specific substances.  
On the other hand, carrier transport proteins of the membrane bind to the substances present at one side of the membrane and deliver them to the opposite side.
 
        
             
        
        
        
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! :)