Answer:
C. The base
Explanation:
The nitrogenous bases, Adenine, Guanine, Thymine and Cytosine in DNA are the variable elements in the nucleotides. Nucleotides are constituted by three elements: The sugar (deoxyribose) and the phosphate group constitutes the backbone of the double helix and are constant in all nucleotides. Also, all nucleotides have carbon and nitrogen atoms.