单项选择题
A.open B.close C.drain D.vent
James Watt （）the steam engine in 1796.A.discoveredB.had...
单项选择题James Watt （）the steam engine in 1796.
A.discovered B.had discovered C.invented D.had invented
Energy loses （）friction occurs in every engine.A.becaus...
单项选择题Energy loses （）friction occurs in every engine.
A.because B.thanks to C.dues to D.owing to
The mechanical efficiency of an engine is always less t...
单项选择题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
