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: Deep gorges are formed by flowing rivers through erosion over long periods of time. 
Question: What are formed by flowing rivers through erosion over long periods of time?
[EX A]: deep gorges.

[EX Q]: Fact: Fanning a fire helps it continue to burn. 
Question: What helps a fire continue to burn?
[EX A]: fanning.

[EX Q]: Fact: navigation requires knowing which way to go. 
Question: What requires knowing which way to go?
[EX A]:
navigation.