Understand that DNA is a polymer, which means it is made up of many repeating units called monomers.
Recall the types of biological monomers: monosaccharides (sugars), amino acids (building blocks of proteins), fatty acids (components of lipids), and nucleotides (building blocks of nucleic acids).
Recognize that DNA is a type of nucleic acid, so its monomers must be nucleotides.
Know that each nucleotide in DNA consists of three parts: a sugar (deoxyribose), a phosphate group, and a nitrogenous base.
Conclude that the repeating units that make up DNA are nucleotides, not monosaccharides, amino acids, or fatty acids.