<span>I believe the answer is: D. proteins
The main functions of these proteins is to allow specific substance to pass through the membrane of the cells which needed for the energy formation for cells'functions.It created through the combination of more than 20 amino acids with different functions.</span><span />
        
                    
             
        
        
        
Answer: Cells
Explanation:
The body has levels of organization that build on each other. Cells make up tissues, tissues make up organs, and organs make up organ systems. The function of an organ system depends on the integrated activity of its organs.