* Seed plants are a category of plants that reproduce using seeds.

* Conifers are a group of seed plants characterized by their cone-shaped structures that hold their seeds. Examples include pine trees, fir trees, and spruce trees.

The other options are not seed plants:

* Horsetails are vascular plants but reproduce using spores, not seeds.

* Mosses are non-vascular plants that also reproduce using spores.

* Ferns are vascular plants that reproduce using spores.