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.

Fact: infection can cause inflammation. 
Question: _can cause inflammation?
Infection.

Fact: An automobile engine works by summing kinetic energy and potential energy. 
Question: What works by summing kinetic energy and potential energy?
an automobile engine.

Fact: Underground systems grow in width and length. 
Question: What grow in width and length.?

underground systems.