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

Q: The cells in the follicle undergo physical changes and produce a structure called a corpus luteum.

A: The cells in the follicle undergo physical changes and produce a structure called a what?
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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: Loss of energy is the reason that food chain typically has few levels.

A:
Loss of energy is the reason that what typically has few levels?
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