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

Ex Output:
navigation.


Ex Input:
Fact: the key cells involved in the immune response are produced in the bone marrow. 
Question: where are the key cells involved in the immune response produced in?

Ex Output:
bone marrow.


Ex Input:
Fact: Buses are used to move people. 
Question: What are buses often used for?

Ex Output:

to move people.