问题
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A gear pump belongs to _____ according to its working principle.
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Communities are part of everyday life and have positive()on its members.A. affectsB.
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An advantage of a helical gear pump over a simple gear pump is that the helical gear pump
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The output volume of a positive fixed displacement pump can be changed only by _____.A.cha
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The gear pump belongs to the () pump.A.positive displacementB.reciprocatingC.centrifugal
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()are used for backing up large amount of data. A. KeyboardB. Hard disksC. CPUD. Displ