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Some people ______ down lots of trees along the river for the past two weeks.

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Natural resource managers ______ the needs and behaviors of wildlife.

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Scientists have been studying different ecologies ______ the 20^th century.

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Naturally, many different species in this freshwater ecosystem share the same kind of ______.

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The national park was established to ______ the ecosystem of the limestone forests.

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The ______ living by the river has been uprooted and then transported away.

The new varieties of rice grow well ______ in poor soil.

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Scientists have been studying the elements that affect the develop of the native species.