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: gases from burning coal causes precipitation which pH is 5.7 or lower. 
Question: Gases from what causes precipitation where the pH is 5.7 or lower?
[EX A]: burning coal.

[EX Q]: Fact: force causes the speed of a crystal ball to increase. 
Question: What can force affect the speed of?
[EX A]: a crystal ball.

[EX Q]: Fact: A force that keeps species evolving increases the productivity and stability of ecosystems. 
Question: A force that keeps species what increases the productivity and stability of ecosystems?
[EX A]:
evolving.