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: roundworms may be free-living or live off a host. 
Question: aside from free-living, where else can roundworms exist?
live off a host.

Fact: passive immunity lasts only as long as the antibodies survive in blood. 
Question: passive immunity lasts only as long as the antibodies survive where?
blood.

Fact: Coal can be used for cooking food. 
Question: Food can be cooked using what?

Coal.