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: You call a substance that is not an acid or a base neutral.

Answer: What do you call a substance that is not an acid or a base?


Question: The outer layer of the sun is made up of plasma.

Answer: What is the outer layer of the sun made up of?


Question: When the core of a star begins to run low on hydrogen, it contracts.

Answer:
What happens to the core of a star when it begins to run low on hydrogen?