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.

[Q]: Fact: A thing arranged in clusters mostly contain instructions for a single protein. 
Question: How often does a thing arranged in clusters contain instructions for a single protein?
[A]: mostly.


[Q]: Fact: Starfish lack respiratory and excretory systems. 
Question: What is an example of an animal that lacks a respiratory and excretory system?
[A]: Starfish.


[Q]: Fact: A compound of hydrogen and oxygen causes refraction of light. 
Question: What causes a refraction of light?
[A]:
compound of hydrogen oxygen.