單項(xiàng)選擇題

Pump up the starting air reservoirs to their maximum pressure and （）the air reservoirs and air system.

A.open
B.close
C.drain
D.vent

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單項(xiàng)選擇題

James Watt （）the steam engine in 1796.

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

單項(xiàng)選擇題

Energy loses （）friction occurs in every engine.

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