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

Q: The active transport of ions across the membrane causes an electrical gradient to build up across the plasma membrane.

A: The active transport of ions across the membrane causes an electrical gradient to build up across the what?
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Q: The thalamus helps to regulate consciousness, arousal, and sleep states.

A: What helps to regulate consciousness, arousal, and sleep states?
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Q: Precipitation are a natural process that allows water to return again to the earth’s surface.

A:
What natural process allows water to return again to the earth’s surface?
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