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: Faulting of rock in the Earth's crust can cause a tsunami. 
Question: What can be caused by a faulting of the earth's crust?
[EX A]: a tsunami.

[EX Q]: Fact: when individuals move into or out of a population, it's random. 
Question: what is it when individuals move into or out of a population?
[EX A]: random.

[EX Q]: Fact: Heavy metals are antigens. 
Question: Heavy metals are _.?
[EX A]:
antigens.