Answer:
B.hydrogen bonding within polypeptide strands 
Explanation:
Alpha helix is one of the secondary structures formed by polypeptide chains. It is formed when the backbone of a polypeptide is wound around a longitudinal axis. The side chains of the amino acids are oriented outwards. Alpha helix structure is stabilized by the formation of a maximum number of hydrogen bonds between the amino acids of the chain. The hydrogen atom linked to the electronegative nitrogen atom of a peptide bond form hydrogen bond with the electronegative carbonyl oxygen atom of the fourth amino acid. 
In this way, every peptide bond except the ones present close to each end of the helix take part in hydrogen bonding and stabilize the structure.
 
        
             
        
        
        
<span>They are used because they keep reproducing more of themselves for use when most cells wouldn't !!!!!!!!!!!!</span>
        
                    
             
        
        
        
Answer:
A plant cell is your answer
Explanation:
prosses of elimination
animal cell - dose not have a cell wall
algae cell - its cell wall has more of a bubblelike appearance
bacterium cell - cell wall is not rigid, and color can vary it has more of a lose thread type look.
plant cell - has a green cell wall that is rigid <--- this is your answer