Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: The bird ancestor that lived in trees developed wings, which is commonly associated with birds.

Answer: The bird ancestor that lived in trees developed what feature commonly associated with birds?

Question: Lichens are not a single organism, but rather an example of a mutualism.

Answer: Lichens are not a single organism, but rather an example of a what?

Question: On a global scale, plants and other photosynthetic organisms have generated all of the oxygen in the air.

Answer:
On a global scale, plants and other photosynthetic organisms have generated all of what element in the air?