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.

Example Input: Fact: Hydrogen bonds cause H20 to expand when it freezes. 
Question: What causes H20 to expand when frozen?
Example Output: hydrogen bonds.

Example Input: Fact: if a gas is heated the density decreases. 
Question: What happens to the density of a gas when heated?
Example Output: decreases.

Example Input: Fact: Ethologists usually study how animals behave around germs. 
Question: Ethologists usually study how animals behave around what?
Example Output:
germs.