Which of the following best describes guard hair?

Guard hair is best described as longer, coarser hair that serves a protective function for the animal. In rabbits, guard hairs are typically the outer layer of fur, which helps to shield the softer undercoat from environmental factors such as moisture, dirt, and physical abrasion. This outer layer also plays a role in maintaining the animal's body temperature by allowing for better airflow and insulation underneath.

In contrast, the other options describe different aspects of a rabbit's fur. The undercoat mentioned in the first choice consists of soft and fluffy hairs that provide insulation, but they do not offer the same level of protection as guard hairs. The option referring to hair that cuts easily with grooming does not pertain to the robustness of guard hairs, as these are more durable. Lastly, while the undercoat may insulate against cold rather than heat, guard hair mainly contributes to protection and does not insulate in the same way that the undercoat does. Thus, the defining characteristic of guard hair is its longer, coarser texture that provides essential protection to the rabbit.