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: Solids are categorized by the forces holding the individual atoms, ions, or molecules together.

Answer: What is categorized by the forces holding the individual atoms, ions, or molecules together?

Question: Stringed instruments can help show the relationship between tension and frequencies in strings.

Answer: Stringed instruments can help show the relationship between tension and what in strings?

Question: Archaeans produce methane gas as a waste product.

Answer:
Archaeans produce what kind of gas as a waste product?