Many plants have thorns on their stems or leaves. What is the MOST likely explanation for the evolution of thorns?

a) Thorns help plants produce more food from photosynthesis.

b) Thorns are an example of a mutation that arises in the genetic code of plants.

c) Thorns help plants to conserve resources like water and soil nutrients that may be used by other organisms.

d) Thorns are an adaptation that some plants have evolved in order to discourage herbivores from eating the plant.