Also the alimentary canal or digestive tract
        
             
        
        
        
That would be A. 
Cells have specific receptors for different hormones that allow the intake of them.
        
                    
             
        
        
        
Answer:
 of folded proteins
Explanation:
In Secondary structures; the irregular loops seems to be positioned on the outside of folded proteins while the Alpha and beta sheets is categorically positioned at the centre or interior of the protein.
The loops are positioned on the outside of folded proteins in order for the peptide bonds to be open to form H bonds with water.
 
        
             
        
        
        
Aldosterone from the adrenal gland is the answer