Write a correct answer to the given question based on its associated fact. Make sure that your answer is contained in the associated fact. Don't be creative and introduce any new word that is not mentioned in the associated fact! Remember that the associated fact has been rearranged to form the question. So, the correct answer words must lie within the associated fact. The correct answer can be a word, phrase, or even a sentence.

Q: Fact: living things all require energy conservation as a trait. 
Question: living things all require energy conservation as a what?

A: trait.
****
Q: Fact: expansion can cause fatigue. 
Question: what can cause fatigue?

A: expansion.
****
Q: Fact: treating H2O is used to remove harmful substances before drinking. 
Question: Why do we generally treat H2O?

A:
to drink it.
****