The wavelength measures the distance between two consecutive crests of a wave.
There for it would be 
A crest.
        
                    
             
        
        
        
The structure shown by the red arrow is cell membrane.  
In biology, cell membrane refers to the thin layer, which develops the external boundary of a living cell. It has three primary functions, which are as follows:  
1. It comprises channels and receptors, which permits particular molecules like nutrients, ions, metabolic components, and wastes to pass between the cell and the outside environment.  
2. It prevents toxic components from entering the cell.  
3. They distinguish essential but incompatible metabolic procedures conducted within the cell.  
 
        
                    
             
        
        
        
Ammonia, drain cleaner, baking soda, chalk, toothpaste, Windex, bleach, laundry detergent, shampoo, and egg whites (household base) 
I hope this helps if not I’m sorry
        
             
        
        
        
Im not knowing of this subject but i'm sure your answer is C.) Patterns 
I really hope this helps. Have a nice day.
 
        
             
        
        
        
Cells, metabolism, reproduction, homeostasis, heredity, etc.