instruction:
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: sharks have tails. 
Question: What has a tail?
answer:
sharks.


question:
Fact: Bacteria can cause food to spoil. 
Question: What causes food to spoil?
answer:
Bacteria.


question:
Fact: A decay curve is used to determine the age of fossils. 
Question: What is used to determine the age of fossils?
answer:

a decay curve.