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.
--------
Question: Fact: Mammals generate heat mainly by burning calories. 
Question: Mammals generate heat mainly by what?

Answer: burning calories.


Question: Fact: Irradiating food can be used to kill something that causes fermentation in the food. 
Question: Irradiating food can be used to kill what in the food?

Answer: Something that causes fermentation.


Question: Fact: Fertilisation is a key feature of roundworm reproduction. 
Question: What has to happen for roundworms to reproduce?

Answer:
Fertilization.