Which Observation BEST Illustrates the Concept of Energy

Which observation BEST illustrates the concept of energy?

A) Despite day-to-day variability in how much food is eaten, most people maintain a fairly constant baseline body weight.
B) Body temperature is always maintained at a constant level.
C) Despite voracious appetites, ob/ob mice display characteristics that are very similar to that of a starving animal.
D) Excess calories are stored in adipose tissue.