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.

[EX Q]: Fact: expansion can cause fatigue. 
Question: what can cause fatigue?
[EX A]: expansion.

[EX Q]: Fact: plants are sensitive to darkness. 
Question: What are plants sensitive to?
[EX A]: darkness.

[EX Q]: Fact: greenhouse gas concentrations in the air have increased over the last decade dramatically. 
Question: What have increased over the last decade dramatically?
[EX A]:
greenhouse gas concentrations.