When a science teacher talks about a machine’s efficiency, what is she comparing?
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A. the useful energy put out by the machine and the energy put into the machine

B. the non-useful energy put out by the machine and the energy put into the machine

C. the thermal energy put out by the machine and the energy put into the machine

D. the non-useful energy put out by the machine and the useful energy put out by the machine

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Mechanics use a pulley to lift an engine out of a car. How could they make the pulley more efficient?
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A. clean and oil the pulley’s axle

B. use a longer rope or cable

C. raise the pulley’s wheel

D. lower the pulley’s wheel