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: A collapsing nebula leads to nuclear fusion process.

Answer: A collapsing nebula leads to what process?


Question: Control rods play an important role in the modulation of the nuclear chain reaction.

Answer: What play an important role in the modulation of the nuclear chain reaction?


Question: The water cycle involves movement of water between air and land.

Answer:
The water cycle involves movement of water between air and what?