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: Vertebrates are all chordates that have a spinal column. 
Question: What do all vertebrates have that invertebrates don't?

Answer: a spinal column.


Question: Fact: temperature can change the state of matter. 
Question: What can change the state of matter?

Answer: temperature.


Question: Fact: fat is used to keep humans warm. 
Question: what uses fat to keep warm?

Answer:
humans.