单项选择题 When inspecting piston rings through the ports of a two-stroke/cycle diesel engine, black areas on the sealing surfaces are the result of （）

单项选择题 Visual inspection of chrome-plated piston compression rings reveals a black ring face at the position of the cylinder liner portsThis condition indicates a ring which（）

单项选择题 A bright shiny appearance of the sealing surfaces on diesel engine compression rings indicates（）