Here's why:

* Monomer: A monomer is a small molecule that can join with other similar molecules to form a larger polymer chain.

* DNA and RNA: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polymers made up of long chains of nucleotides.

* Nucleotide: Each nucleotide consists of three parts:

* A sugar molecule (deoxyribose in DNA and ribose in RNA)

* A phosphate group

* A nitrogenous base (adenine, guanine, cytosine, thymine in DNA; adenine, guanine, cytosine, uracil in RNA)

So, nucleotides are the building blocks of DNA and RNA.