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: cell regeneration requires rest. 
Question: what requires rest?

Answer: cell regeneration.


Question: Fact: Birds have high levels of intelligence and are wired to learn. 
Question: What have high levels of intelligence and are wired to learn?

Answer: birds.


Question: Fact: a black hole is not visible. 
Question: what are not visible?

Answer:
black hole.