Turn the given fact into a question by a simple rearrangement of words. This typically involves replacing some part of the given fact with a WH word. For example, replacing the subject of the provided fact with the word "what" can form a valid question. Don't be creative! You just need to rearrange the words to turn the fact into a question - easy! Don't just randomly remove a word from the given fact to form a question. Remember that your question must evaluate scientific understanding. Pick a word or a phrase in the given fact to be the correct answer, then make the rest of the question. You can also form a question without any WH words. For example, "A radio converts electricity into?"

Q: Fact: tree squirrels generate heat mainly by keeping their metabolic rate high.

A: What generate heat mainly by keeping their metabolic rate high?
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Q: Fact: isotopes are used to determine the age of fossils.

A: what is used to determine the age of fossils?
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Q: Fact: The key cells involved in the immune response produce antibodies.

A:
The cells that produce antibodies are key in what system?
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