Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: Virtually all aquatic organisms depend directly or indirectly on protists for food.

Answer: Virtually all aquatic organisms depend directly or indirectly on what for food?


Question: Limestone is insoluble in water, so acid can dissolve it.

Answer: Limestone is insoluble in water, so what can dissolve it?


Question: Weight is the term for the measure of the force of gravity pulling down on an object.

Answer:
What is the term for the measure of the force of gravity pulling down on an object?