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.
--------
Question: Fact: Food can be cooked on metal. 
Question: Which surface can food be cooked on?

Answer: Metal.


Question: Fact: skin is cooled by evaporation. 
Question: What cools the skin?

Answer: evaporation.


Question: Fact: A valley are formed by erosion. 
Question: How does water cause a valley to form?

Answer:
By the process of erosion.