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: large animals that roamed the earth were replaced with mammals after their extinction. 
Question: large animals that roamed the earth were replaced with what after their extinction?
mammals.

Fact: Viruses are viewed by illuminating electrons. 
Question: What of the following can only be viewed by illuminating electrons?
viruses.

Fact: Flowers are specialized reproductive organs. 
Question: What are flowers for?

Reproductive organs.