單項(xiàng)選擇題

James Watt （）the steam engine in 1796.

A.discovered
B.had discovered
C.invented
D.had invented

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單項(xiàng)選擇題

Energy loses （）friction occurs in every engine.

A.because
B.thanks to
C.dues to
D.owing to

單項(xiàng)選擇題

The mechanical efficiency of an engine is always less than 100% （） losses occurring in the form friction.

A.because
B.since
C.due to
D.owing to

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