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: Some compounds form rigid frameworks called crystals.

Answer: Some compounds form rigid frameworks called what?


Question: Skeletal muscles must work in pairs to move bones back and forth at a joint because they can only contract.

Answer: Skeletal muscles must work in pairs to move bones back and forth at a joint because they can only do what?


Question: Global winds do you call winds that occur in belts that go all around the planet.

Answer:
What do you call winds that occur in belts that go all around the planet?