instruction:
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.
question:
Fact: Passenger pigeons could not produce enough offspring. 
Question: What could not produce enough offspring?
answer:
passenger pigeons.


question:
Fact: Energy enters ecosystems from the sun. 
Question: The sun contributes what to ecosystems?
answer:
energy.


question:
Fact: sharing of electrons forms a bond. 
Question: What is shared to form a bond?
answer:

electrons.