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: Bacteria is usually the prey of a protist.

Answer: What is usually the prey of a protist?


Question: Low energy causes waves to bring sand up onto the beach during summers.

Answer: What causes waves to bring sand up onto the beach during summers?


Question: Experiments have shown that acceleration is exactly inversely proportional to mass, just as it is exactly linearly proportional to the net external force.

Answer:
Experiments have shown that acceleration is exactly inversely proportional to mass, just as it is exactly linearly proportional to what?