单项选择题
A.coming up from the BDC B.coming up from the TDC C.coming down from the BDC D.coming down from the TDC
Pump up the starting air reservoirs to their maximum pr...
单项选择题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
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
