Which phrase listed below best describes the function of the digestive system?
a. to filter out waste from the blood
b. to remove waste from the body
c. to break down food into nutrients
d. to protect the body against germs

The best answer is C - to break down food into nutrients.

The digestive system  breaks down food  into its simplest form that cell are able to utilize  for energy.  Food is broken down into its monomer units. Proteins are broken down into amino acids, lipids are broken down into fatty acids and glycerol and carbohydrates are broken down into glucose.

Glucose is then absorbed into the blood and transported to every cell in the body. The cells take in glucose and use it as fuel and raw material  in the process of cellular respiration. From one molecule of glucose, 36 to 38 molecules of ATP ( the form of energy used by cells) are produced.