Final answer:
The epidermis contains guard cells, epidermal cells, and trichomes, all of which contribute to the protection, gas exchange, and water regulation of the plant.
Step-by-step explanation:
The epidermis is the outer layer of cells covering the plant and serves multiple functions to protect and maintain the plant's physiology. The correct final answer to what is in the epidermis is D) All of the above, which includes guard cells, epidermal cells, and trichomes. Guard cells are specialized cells that surround stomata, playing a crucial role in gas exchange by opening and closing these pores. Epidermal cells are the most numerous and make up the bulk of the epidermis, which secretes a waxy cuticle to reduce water loss. Trichomes are hair-like structures that help reduce transpiration, increase reflectance, and often store defensive compounds to protect the plant from herbivores.