单项选择题
The four-stroke cycle begins with the piston （）.
A.coming up from the BDC B.coming up from the TDC C.coming down from the BDC D.coming down from the TDC
单项选择题 Pump up the starting air reservoirs to their maximum pressure and （）the air reservoirs and air system.
单项选择题 James Watt （）the steam engine in 1796.
单项选择题 Energy loses （）friction occurs in every engine.
