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.

[Q]: Fact: Vertebrates are all chordates that have a spinal column. 
Question: What do all vertebrates have that invertebrates don't?
[A]: a spinal column.


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


[Q]: Fact: Erosion can cause seismic vibrations which are triggering mechanisms. 
Question: What can cause seismic vibrations, which are triggering mechanisms?
[A]:
erosion.