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: respiration requires a certain amount of air.

A: What requires a certain amount of air?
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Q: Fact: Deep gorges are formed by flowing rivers through erosion over long periods of time.

A: What are formed by flowing rivers through erosion over long periods of time?
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Q: Fact: Lung cancer is most often caused by cigarettes.

A:
What is lung cancer most often caused by?
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