A Young Medical Student Has Removed a Tendon, Intestine, and Heart

A young medical student has removed a tendon, intestine, and heart from a cadaver. When he flattens all of these structures (and stretches them out to their utmost extent) , he notices that the intestine is by far the largest structure. Why?

A) The intestine is the site of all bulk flow carried out in the human body, and must be large in order to supply the entire body with nutrients.
B) The intestine is the source of all materials transported by means of bulk flow (i.e., it produces hormones, absorbs nutrients, and is the site where oxygen diffuses into the bloodstream) .
C) The intestine must have a large surface area over which nutrients derived from food can diffuse into the bloodstream.
D) The intestine must have a large surface area to produce hemoglobin, which then binds to food particles and transports them throughout the body.