What is the primary function of the large intestine?

The primary function of the large intestine is the absorption of water. As food is processed in the gastrointestinal tract, particularly in the small intestine, it results in a mixture of undigested food material and liquid. The large intestine then plays a crucial role in reabsorbing water from this mixture, which helps to form solid waste (feces) and maintain the body's fluid balance. This process is vital for preventing dehydration and ensuring that the body retains essential fluids.

While the large intestine does have some involvement in the production of certain vitamins, such as vitamin K by gut bacteria, this is a secondary function compared to its main role in water absorption. The large intestine is not primarily involved in the digestion of proteins or the absorption of nutrients, both of which predominantly occur in the small intestine. Therefore, the choice reflecting the large intestine's primary function focuses on its vital role in absorbing water from indigestible food matter.