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

Q: Compression zones is the opposite of rarefaction zones, where air molecules in waves are loosely packed.

A: What is the opposite of rarefaction zones, where air molecules in waves are loosely packed?
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Q: Present-day plants that have a complex vascular tissue system are called vasuluar plants.

A: Present-day plants that have a complex vascular tissue system are called what kind of plants?
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Q: Gases in the air allows us to hear sound.

A:
What in the air allows us to hear sound?
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