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work-and-energy-n05!1
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characteristics-of-sound!1
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electronic-force!3
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electronic-force!2
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non-contact-force!3
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non-contact-force!2
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electronic-force!1
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non-contact-force!1
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natural-resources!2
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natural-resources!1
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playing-with-numbers!2
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playing-with-numbers!1
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electronic-force!4