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wheels-reduce-friction-n03!1 Wheels reduce friction
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wheels-reduce-friction-n03!2 Wheels reduce friction
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non-contact-force!2
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non-contact-force!3
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electronic-force!2
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electronic-force!3
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electronic-force!4
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electronic-force!5
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how-does-air-get-polluted-k1!2
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electici-crcuit-and-electric-switch!5
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characteristics-of-sound!1
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electici-crcuit-and-electric-switch!6
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work-and-energy-n05!1
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motion-n02!1
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symbols-of-electric-current!1