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

Q: A concave lens is thicker at the edges than it is in the middle.

A: What type of lens is thicker at the edges than it is in the middle?
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Q: Atp or adenozine triphosphate is used for most energy functions in organisms.

A: What molecule is used for most energy functions in organisms?
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Q: The brain stem regulates the rate of breathing.

A:
Which part of the brain regulates the rate of breathing?
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