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Turning off the light when leaving a room is an example of

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What most likely happens to soil when crops are not rotated from year to year?

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In Costa Rica a small tree, the acacia, provides shelter and food for ants. The ants protect the acacia by removing other insects and vines that might harm it. Which term best describes the relationship between the acacia and the ants?

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Which region of the Milky Way contains a population that consists mostly of old stars?