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.

[EX Q]: Fact: decomposition increases amount of organic matter in dirt. 
Question: What increases amount of organic matter in dirt?
[EX A]: decomposition.

[EX Q]: Fact: Water can make soil from rocks. 
Question: What causes rocks to be worn into soil?
[EX A]: Water.

[EX Q]: Fact: The bonds of that which when heavy is Deuterium cause water to expand when it freezes. 
Question: The bonds of that which when heavy is Deuterium cause what to expand when it freezes?
[EX A]:
water.