Here's why:

* Enzymes are biological catalysts that speed up chemical reactions. They are proteins (or in some cases RNA molecules) that have a specific three-dimensional shape that allows them to bind to specific molecules (substrates) and facilitate their transformation.

* RNA polymerase is a complex enzyme responsible for transcribing DNA into RNA. It binds to DNA, separates the two strands, and uses one strand as a template to build a complementary RNA molecule.

So, RNA polymerase is an enzyme because it acts as a catalyst to facilitate the process of transcription, which is a chemical reaction.