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: food is irradiated for space travel. 
Question: what food is required for space travel?
irradiated.

Fact: gases from burning coal causes precipitation which pH is 5.7 or lower. 
Question: Gases from what causes precipitation where the pH is 5.7 or lower?
burning coal.

Fact: Healing of fractures requires cells specialized in bone remodeling. 
Question: Healing of fractures requires cells specialized in?

bone remodeling.