Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: Oxygen gas is given off by plants.

A: Which gas is given off by plants?
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Q: Negative growth rate results when birth rates fall even lower than death rates.

A: What results when birth rates fall even lower than death rates?
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Q: Dinosaurs filled the niches that mammals fill today during the mesozoic era.

A:
Dinosaurs filled the niches that mammals fill today during which era?
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