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: Coal is used to produce the movement of electrons by burning in coal-fire power stations. 
Question: Coal is used to produce the movement of electrons by what in coal-fire power stations?
burning.

Fact: Food can be cooked on metal. 
Question: Which surface can food be cooked on?
Metal.

Fact: keratin protects fish from predators and parasites and reduce friction with the water. 
Question: What protects fish from predators and parasites and reduces friction with the water?

keratin.