Answer:
a. adenine and guanine
Explanation:
A purines nucleotide is a combination of the heterocyclic aromatic rings, the imidazole and pyrimidine ring.
<span>A group of cells that function together to perform a special activity is known as a tissue. Epithelial tissues are the tissues that lines inside of hollow organs. </span><span> Epithelial tissues covers body surfaces; lines the body cavities and hollow organs.</span>
Im pretty the term that describes it is
Soil Structure