What is the primary function of the digestive system?

The primary function of the digestive system is to break down food into nutrients. This process is essential for the body to obtain the necessary energy and materials it needs to function properly. When food is ingested, the digestive system employs various organs, such as the stomach and intestines, to mechanically and chemically process the food. This breakdown of food allows for the extraction of nutrients, which are then absorbed into the bloodstream and delivered to cells throughout the body, supporting vital functions.

The other options address important bodily functions but do not pertain directly to the digestive system's primary role. Eliminating waste is a significant function of the excretory system, circulating blood falls under the cardiovascular system, and regulating body temperature is primarily managed by the integumentary and thermoregulatory systems. Therefore, option C accurately captures the key purpose of digestion.