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.

Ex Input:
Fact: if a gas is heated the density decreases. 
Question: What happens to the density of a gas when heated?

Ex Output:
decreases.


Ex Input:
Fact: navigation requires knowing which way to go. 
Question: What requires knowing which way to go?

Ex Output:
navigation.


Ex Input:
Fact: when a human moves, chemical energy is converted to mechanical energy. 
Question: what moves by converting chemical energy into mechanical energy?

Ex Output:

humans.