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: a light bulb is used for seeing at night. 
Question: a light bulb is used for seeing?
[EX A]: at night.

[EX Q]: Fact: abalone  are invertebrates such as the common snail. 
Question: What are invertebrates such as the common snail?
[EX A]: abalone.

[EX Q]: Fact: To measure the hardness of materials, scratching those materials is necessary. 
Question: What is necessary to measure the hardness of materials?
[EX A]:
scratching.