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.

Fact: Skin color is influenced by environmental factors. 
Question: what is influenced by environmental factors?
skin color.

Fact: Mammals generate heat mainly by burning calories. 
Question: Mammals generate heat mainly by what?
burning calories.

Fact: Wells can be filled with precipitation that falls on land and soaks into the ground. 
Question: What can be filled with precipitation that falls on land and soaks into the ground?

wells.