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: Vertebrates have a complete digestive system and a closed circulatory system. 
Question: vertebrates have a complete digestive system and a what?
closed circulatory system.

Fact: sunlight causes rainbows. 
Question: what causes rainbows?
sunlight.

Fact: phones require electrical energy to function. 
Question: What do phones require to function?

electrical energy.