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: most bigger cities require vehicles. 
Question: What do most bigger cities require?

Answer: vehicles.


Question: Fact: prokaryotes can make proteins. 
Question: what can make proteins?

Answer: prokaryotes.


Question: Fact: burning fossil fuels are used to produce electricity. 
Question: What are burned to produce electricity?

Answer:
fossil fuels.