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: Birds have backbones. 
Question: What animals have a backbone?
Birds.

Fact: A bicycle is a vehicle that requires smooth surfaces. 
Question: What kind of surface does a bicycle require to ride on?
smooth.

Fact: being exposed to wind can cause disturbance of a land surface. 
Question: what can being exposed to wind cause?

disturbance of land surface.