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: Water can make soil from rocks. 
Question: What causes rocks to be worn into soil?

Answer: Water.


Question: Fact: Cells are formed into tissues and tissues form the liver. 
Question: The liver is formed after cells for into?

Answer: tissue.


Question: Fact: expansion can cause fatigue. 
Question: what can cause fatigue?

Answer:
expansion.