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: food can cause illness. 
Question: What is a source of  illness?
food.

Fact: Passenger pigeons could not produce enough offspring. 
Question: What could not produce enough offspring?
passenger pigeons.

Fact: Foxes conserve body heat with their hair or fur. 
Question: What conserve body heat with their hair or fur?

foxes.