The correct answer is - physically dettering herbivory, protection from frost, and minimizing evaporation.
The plants have developed multiple traits that help them in multiple different circumstances, and some of those traits are the thorns and the hairs on their steams and leaves.
The thorns primarily serve for protection of the plant. They are very sharp and give a painful sting (occasionally poisonous one), so they are a physical protection from the herbivores that would try to eat parts of the plants.
The hairs have multiple functions. They are like a coat that helps the plant to not be affected by frost, help to stop the evaporation, and also partially manage to stop most of the insects that feed on plants.