Given a scientific passage and an answer, generate a question for the given answer.

Q: Passage: Most fungi get organic compounds from dead organisms. Fungi use their hyphae to penetrate deep into decaying organic matter. They produce enzymes at the tips of their hyphae. The enzymes digest the organic matter so the fungal cells can absorb it. Fungi are the main decomposers in forests. They are the only decomposers that can break down cellulose and wood. They have special enzymes for this purpose. Answer: hyphae

A: What do fungi use to penetrate deep into decaying matter?
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Q: Passage: Acidity is measured on a pH scale. Rain that is 5.0 or less on that scale is considered acid rain. Answer: ph scale

A: Acidity is measured on what kind of scale?
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Q: Passage: Primary succession occurs in an area that has never before been colonized. Pioneer species include bacteria and lichens that can grow on bare rock and help make soil. Answer: primary succession

A:
What kind of succession occurs in an area that has never before been colonized?
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