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: Natural magnetism is used for pointing north in a surveying tool. 
Question: Who would use a tool that uses a magnet that points north?
Example Output: surveyor.

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: Acid changes the color of certain paper at different acidity. 
Question: Acid changes the color of what when acidity reaches certain amounts?
Example Output:
paper.