单项选择题
（）the moveable plate and floating ring inside the pump is very difficult.
A.Having adjusted B.Being adjusted C.To adjust D.Adjusted
单项选择题 The four-stroke cycle begins with the piston （）.
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.
