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: 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: All birds have backbones. 
Question: Which animal has a backbone?
bird.

Fact: Birds steer by using muscles in their chest. 
Question: Birds steer by using muscles in their what?

chest.