Which Statement Can Be Used as Evidence That Living Systems

Which statement can be used as evidence that living systems obey the first law of thermodynamics?

A) Metabolic processes in cells rely on the coupling of exergonic reactions to endergonic reactions.
B) Not all of the energy entering an organism can be converted to forms of energy that are useful to the organism.
C) All of the energy taken in by an organism can be accounted for after it is transformed to other forms of energy, including heat.
D) Living things require a constant input of energy to maintain the living state.
E) In biological transformations involving a transfer of energy, entropy increases.