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: Each starfish arm contains part of the water vascular system. 
Question: Where does a starfish have its water vascular system?
in its arms.

Fact: male dogs use natural aphrodisiacs in urine to mark their territory. 
Question: what do male dogs use in their urine to mark their territory?
natural aphrodisiacs.

Fact: frogs need their skin to survive. 
Question: What do frogs need to survive?

skin.