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

Q: The size and symmetry of a beetle’s or an elk’s antlers or a grasshopper’s song communicate rather clearly their state of health.

A: The size and symmetry of a beetle’s or an elk’s antlers or a grasshopper’s song communicate rather clearly their state of what?
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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: The behavior of ideal gases is explained by kinetic molecular theory.

A:
The behavior of ideal gases is explained by what theory of gases?
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