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: The crystallized rocks are made by lava from the mantle. 
Question: Where does the lava come from that makes igneous rocks?
answer:
Mantle.


question:
Fact: Viruses are viewed by illuminating electrons. 
Question: What of the following can only be viewed by illuminating electrons?
answer:
viruses.


question:
Fact: mutation is the basis for natural selection. 
Question: what is the basis for natural selection?
answer:

mutation.