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.
--------
Question: Fact: Machines can cause objects to change shape. 
Question: What can cause objects to change shape?

Answer: Machines.


Question: Fact: A vehicle in use requires navigation. 
Question: A vehicle in use requires?

Answer: navigation.


Question: Fact: Frogs breathe through their skin which is porous. 
Question: Frogs breathe through their skin, which is what?

Answer:
porous.