Here's why:

* Nucleic acids are polymers, not monomers. They are made up of smaller repeating units called nucleotides.

* Nucleotides are the monomers of DNA and RNA. They consist of three parts:

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

* A phosphate group

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

So, to summarize:

* DNA and RNA are nucleic acids.

* Nucleotides are the monomers that make up DNA and RNA.