| 21. | However, this is a natural system and temperatures will vary.
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| 22. | Past development hugely altered the natural systems of the region.
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| 23. | Culture was now just another natural system that could be explained in mathematical terms.
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| 24. | Alaska has strict laws governing the protection of natural systems such as salmon streams.
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| 25. | Dynegy got the Northern Natural system out of a broken merger agreement with Enron.
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| 26. | These changes could affect the availability of freshwater for natural systems and human uses.
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| 27. | For natural systems, those data are very difficult to collect.
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| 28. | The losers will be the natural systems and human environment of the Pacific Northwest.
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| 29. | Complex natural systems arise from millions upon millions of organisms living, dying, and evolving.
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| 30. | Some experts say natural systems are intrinsic to psychological well-being.
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