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: expansion can cause fatigue. 
Question: what can cause fatigue?
Example Output: expansion.

Example Input: Fact: protective plates over the ends of the fingers become more brittle with age. 
Question: What do fingers have over the ends that become more brittle with age?
Example Output: protective plates.

Example Input: Fact: animals in the Phylum Porifera are a source of food for many species of fish. 
Question: animals in the Phylum Porifera are a source of what for many species of fish?
Example Output:
food.