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: heat is detected by sensory nerve cells. 
Question: What is detected by sensory nerve cells?
heat.

Fact: Scraping oneself on surfaces or things that have germs may cause infection. 
Question: Which of the following may cause infection?
Germy surfaces.

Fact: Wave action can cause rocks to contact over time. 
Question: Wave action causes?

contact between rocks.