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: thirst is used to make an animal realize that it needs to replenish H2O in its body. 
Question: Thirst shows an animal that it needs what?

A: H2O.
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Q: Fact: x-rays are used in oncology. 
Question: what are used in oncology?

A: x-rays.
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Q: Fact: Bottleneck effect occurs with external migration. 
Question: Bottleneck effect can occur with?

A:
external migration.
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