OPTIONS: [i] squids [ii] animals [iii] water vapor [iv] batteries [v] humans [vi] bacteria [vii] the Sun [viii] Clams

You are presented with the quiz "What require energy for survival?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "living things all require energy for survival" and "bacteria are simple, as living things go". So, what's the best answer to the question?
Answer:
[vi]