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: Phenotypic expression of skin color varies over a wide range. 
Question: Phenotypic what of skin color varies over a wide range?
[A]: expression.


[Q]: Fact: rivers can slowly dissolve carbon in sedimentary rock. 
Question: what can slowly dissolve carbon in sedimentary rock?
[A]: rivers.


[Q]: Fact: Head hair can help prevent hypothermia. 
Question: Head hair can help prevent?
[A]:
hypothermia.