Derived from a 6 membered ring. contains cytosine, thymine, and uracil.
a. macromolecules
b. nucleotides
c. pyrimidine
d. purine
e. x-ray crystallography

b. Nucleotides  

Explanation:

Nucleic acids are examples of structures formed from nucleotides. And in relation to the composition of DNA, we have the formation of the largest cellular macromolecule, all formed by nucleotides.

The nucleotide is a group formed by the association of 3 molecules - a nitrogen base, a phosphate group and a pentose glycide. Thus, we may have variations within these ligands, such as: in DNA we have the presence of pentose deoxyribose, while in RNA we have the presence of pentose ribose.

The nucleotides have differences in relation to its nitrogen base, which can be purine or pyrimidine. Purine bases vary in Adenine and Guanine, while pyrimidine bases are classified in Thymine, Uracil and Cytosine. Purine and pyrimidine bases are complementary and each have specific binders. Thus, we have that the purine base Adenina, binds with the pyrimidine bases Timina and Uracila, while the base Guanina binds exclusively to Cytosine and vice versa.