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.

[EX Q]: Fact: many plants respond to the days growing shorter in September by going dormant. 
Question: when do plants respond to shorter days by going dormant?
[EX A]: September.

[EX Q]: Fact: boulders are formed by snow, ice, and rock melting sometimes. 
Question: what melts sometimes to form boulders?
[EX A]: snow, ice, and rock.

[EX Q]: Fact: sight involves the retina. 
Question: what involves the retina?
[EX A]:
sight.