Answer:
Because it is a solid that has trapped air with the water molecules in cold temperature thus creating a hard solid.
 
        
                    
             
        
        
        
The structure of DNA is double helix which looks like twisted ladder. The sides of the DNA molecule, the rails of the ladder are composed of alternate phosphate and sugar molecules.
 
        
             
        
        
        
Your answer is D. Nucleotide
        
             
        
        
        
No I think you need to do some more research