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

Q: Pyramid ecosystem is used to show energy flow through the trophic levels.

A: What is used to show energy flow through the trophic levels?
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Q: Constructive forces type of forces are involved when deposited rock forms deltas or barrier islands.

A: What type of forces are involved when deposited rock forms deltas or barrier islands?
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Q: Excretory system lets flatworms maintain a proper balance of water and salts.

A:
What system lets flatworms maintain a proper balance of water and salts?
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