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.

Input: Consider 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?

Output: bone marrow.


Input: Consider Input: Fact: fields make compasses point north. 
Question: What makes compasses point north?

Output: fields.


Input: Consider Input: Fact: Unequal heating of Earth's surface by the Sun can cause some geographical areas to evolve into deserts. 
Question: What can happen to some geographical areas due to uneven heating of Earth's surface by the sun?


Output: Deserts can form.