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: Cars damage the environment by causing an excess of contaminants. 
Question: How do cars damage the environment?
Emitting an excess of contaminants.

Fact: a light bulb is used for seeing at night. 
Question: a light bulb is used for seeing?
at night.

Fact: One of the oldest forms of energy used by humans can be used to produce electricity. 
Question: One of the oldest forms of energy used by humans can be used to produce what?

energy.