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: muscles contain cells. 
Question: What do muscles contain?

Answer: cells.


Question: Fact: certain Steel products have a positive impact on the environment. 
Question: certain Steel products have a positive impact on what?

Answer: environment.


Question: Fact: mussels feed on plankton and nonliving organic matter. 
Question: What feeds on plankton and nonliving organic matter?

Answer:
mollusks.