Which of the following fibers is considered an animal fiber?

Silk is considered an animal fiber because it is derived from the cocoon of the silkworm, an insect that belongs to the animal kingdom. Animal fibers originate from various sources, including the hair, fur, skin, or secretions of animals. Silk is unique among fibers for its luxurious feel, durability, and natural sheen, which are all attributed to its protein-based composition.

In contrast, cotton is a plant fiber sourced from the cotton plant's seed fibers, linen is made from the fibers of the flax plant, and rayon is a semi-synthetic fiber produced from cellulose, typically extracted from wood pulp. Therefore, silk stands out as the only option that originates from an animal source, confirming its classification as an animal fiber.