Which component is part of an epoxy?

The correct choice is based on the understanding of epoxy formulations. An epoxy is a type of thermosetting polymer that typically consists of two components: a resin and a hardener (or binder). When these two components are mixed together, a chemical reaction occurs that results in a hardened material, providing strength and durability. This characteristic of requiring a mixture of distinct components is fundamental to how epoxy works, making option B the correct choice.

In contrast, the other options describe different types of formulations that do not fit the definition of an epoxy. A single-component base refers to products that are ready to use without mixing, which does not apply to epoxy systems. Water-based paint represents a different category of coatings that do not harden through the same chemical process as epoxy. Lastly, a one-part sealant is a formulation that does not require mixing and often cures through solvent evaporation or exposure to moisture, which is also distinct from the epoxy process.