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: Nests are used to protect eggs from predators and extreme temperatures. 
Question: What are used to protect eggs from predators and extreme temperatures?
nests.

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: Polar bears can generate heat by shivering. 
Question: What can polar bears do to generate heat?

shiver.