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: Mammals can generate little bursts of energy by shivering. 
Question: What can a mammal produce by shivering?
energy.

Fact: Using hydropower reduces greenhouse gases. 
Question: What does hydropower help reduce?
Greenhouse gases.

Fact: P-waves and S-waves can be traced back to faulting of rock in Earth's crust. 
Question: The origin of P-waves and S-waves can be traced back to what?

Faulting of rocks in the crust.