For Nutritional Purposes, Which Statement Most Closely Defines the Function

For nutritional purposes, which statement most closely defines the function of measurable energy (in calories) for different foods?

A) The portion of the partial energy of a diet that is derived from animal proteins
B) The portion of the partial energy of a diet that is consumed
C) The portion of the total energy of a diet that is expended from the body
D) The portion of the total energy of a diet that is retained within the body