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: expansion can cause fatigue. 
Question: what can cause fatigue?
[A]: expansion.


[Q]: Fact: Condensation causes sun blocking and temperature drops. 
Question: What causes sun blocking and temperature drops?
[A]: condensation.


[Q]: Fact: algae plays significant roles as food in acquatic ecosystems. 
Question: what does algae play a significant role as in aquatic ecosystems?
[A]:
food.