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: Single-celled organisms and multicellular organisms have this in common: both have a way to get rid of waste materials.

A: Which characteristic do single-celled organisms and multicellular organisms have in common?
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Q: Homes and transportation use half (fifty) percent of all energy in the u.s.

A:
Homes and transportation use what percent of all energy in the u.s.?
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