Correct Option: D. Rabbits Explanation of the Correct Answer Rabbits are unique among the options provided because they possess a pair of caeca. The caeca (singular: cecum) are two blind-ended pouches located at the junction of the small and large intestines. In rabbits, these structures play a crucial role in their digestive process, particularly because they are herbivores that consume a high-fiber diet.

1. Function of the Caeca in Rabbits:
2. The caeca in rabbits are involved in the fermentation of fibrous plant material. This fermentation process allows rabbits to break down cellulose, a major component of plant cell walls, which is otherwise indigestible.
3. The caeca also produce cecotropes, which are nutrient-rich droppings that rabbits consume directly from their anus. This behavior allows them to re-digest these droppings to extract additional nutrients, particularly vitamins and proteins.
4. Digestive Adaptation:
5. The presence of a pair of caeca is an adaptation that enables rabbits to thrive on a diet that is low in protein and high in fiber. The fermentation process in the caeca helps maximize nutrient absorption from their food.

Explanation of Incorrect Options A. Pigs: - Pigs do not have a pair of caeca. They possess a single cecum, which is a small pouch that aids in the fermentation of food but is not as developed as in rabbits. Pigs are omnivores and have a different digestive system that does not require the same level of fermentation as herbivores like rabbits. B. Cattle: - Cattle are ruminants and have a complex stomach with four compartments (rumen, reticulum, omasum, and abomasum) but do not have a pair of caeca. Instead, they have a single cecum that plays a minor role in their digestion, as most fermentation occurs in the rumen. C. Sheep: - Similar to cattle, sheep are also ruminants and possess a single cecum. Their digestive system is adapted for breaking down fibrous plant material through a multi-chambered stomach, and they do not have a pair of caeca. Summary of Key Points

• Rabbits possess a pair of caeca, which are essential for fermenting fibrous plant material and producing cecotropes.
• Pigs, cattle, and sheep have a single cecum, which is less developed and serves a different function in their digestive processes.
• The caeca in rabbits allow for efficient nutrient absorption from a high-fiber diet, showcasing their unique adaptation as herbivores.

Revision Summary

• Rabbits have a pair of caeca that aid in fiber digestion and nutrient absorption.
• Pigs, cattle, and sheep have a single cecum, not a pair of caeca.
• The caeca in rabbits are crucial for producing cecotropes, which they re-digest for additional nutrients.
• Understanding the digestive adaptations of different farm animals is key in agricultural science.