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.

[Q]: Fact: Exposure to cold can induce many muscle fibers to contract at once. 
Question: Many muscle fibers contracting at once can be induced by?
[A]: exposure to cold.


[Q]: Fact: Cold fronts cause lightning. 
Question: Cold fronts cause what?
[A]: lightning.


[Q]: Fact: the mass of an object causes the attraction exerted by that object. 
Question: What causes the amount of attraction exerted by an object?
[A]:
mass.