单项选择题 In a four-stroke/cycle diesel engine, after the completion of the power stroke, the piston will move（）

单项选择题 A fuel injection valve opening at pressure lower than normal will result in（）.

单项选择题 In a diesel engine, exhaust valves open before the intake ports are uncovered to （） Ⅰ.reduce pumping losses Ⅱ.reduce back pressure