When the engine RPM decreases to 500,stop the engine.当发动机转速下降到 500 时，停止发动机。
A.When stop the engine, make sure that the engine decelerates to,500 RPM. B.If the engine decreases to 500 RPM, you must stop C.When the engine RPM decreases 500, you'd better stop the engine.正确答案A
